With a huge thanks to Jack, four of our changing room group were able to keep meeting and masturbating during the summer holidays.

Every Friday night, his big sister Samantha let him use her flat while she was out at the clubs, allowing him and his friend Steven some time away from their parents. Our fourth member was my best friend Tiff. She had originally said she wasn't keen because she was more interested in having sex than masturbating, but it didn't take much persuasion when I said there would be two boys there.

We were in Samantha's living room on the couches: Jack and Steven on one, Tiff and me on the other. Since we had more time than we were did in the changing room, we could go on for longer. We'd each keep our own genitals stimulated and try to bring ourselves as close as possible to an orgasm without going over the edge. For seventeen-year-olds who normally pleasured ourselves at least once or twice a day, it was a tough call. It was also a little unfair because if us girls accidentally climaxed, we could just start again, while the boys would need time to 'recharge'. To their credit, though, they usually managed to shoot twice in one night, even if the second spurt was never nearly as big as the first.

Once we'd built up some trust with each other, we began to relax the rules so we could touch each other, something that had never been allowed in the changing room. Tiff already took oral contraception, and in preparation for what might happen, I starting taking it too. To be extra safe, however, we still agreed there should be no penetration, and no semen should end up on or in our vaginas.

We also had to be careful to watch our time, as Samantha knew Jack and Steven were there, but not us. We always had to be dressed and away by 2am.

Our sessions always started off with solo masturbation, under our clothes at first, then gradually undressing, all the time holding off orgasm. We would then form opposite-sex pairings, swapping partners after a little while. Each of the boys would touch our breasts and butts, and lick and suck our nipples, while we took a lot of pleasure from running our hands over their toned bodies and gently kissing their chests and tiny nipples. This inevitably evolved into masturbating each other.

When I used to look around the changing room, it seemed every girl had her own particular technique. For example, I rub the ridge of my clit head through the hood in a slight circular motion, while Tiff takes a lot of pleasure from moving a hairbrush handle back and forth inside her. We'd started talking about how we might buy vibrators in secret because we weren't yet eighteen, and it turned out we'd both wanted them for the longest time. Tiff sometimes used the back of an electric toothbrush head with the bristles pointing away from her, but I found the vibration simply wasn't strong enough.

By contrast, it also seemed every boy shared an identical up-and-down technique, but I learnt that wasn't quite the case. Steven liked slower strokes, with his foreskin stretched right back on the down motion, but Jack needed quicker strokes and was too sensitive to have the head fully exposed.

Both giving stimulation and receiving it from another person were reasonably pleasurable, but it's hard to teach someone who doesn't have the same genitals. I also found it a real workout to maintain the big arm movements required to stroke a penis compared to the subtle hand and finger gestures for a clit. Each of us usually ended up finishing ourselves off, except for the one glorious day Steven made Tiff orgasm loudly, then I made Steven shoot. He and I were so proud of ourselves.

We enjoyed more success with dry humping. In our pairs, one or both of us would wear underwear to avoid accidental penetration as we rubbed our genitals up and down over each other. For me, it seemed to work best when the girl kept her panties on and the boy went bareback. I also liked it that way round for another reason.

The first time I'd tasted semen was after getting Steven off. If I'd known he was so close, I would've grabbed a tissue, caught it and cleaned it up, and possibly never have developed my taste for the stuff. Instead, it landed all over the back of my hand. When I went to the bathroom to wash it off, my curiosity kicked in and I licked up half of it, followed by the rest. Afterwards, I told Tiff in private what I'd done. 'Eww,' she said, that's disgusting. How could you do that?' I encouraged her to try it the next Friday, but she never did.

By the time we'd progressed to humping, there was no secret about my taste for semen. When one of the boys spurted on my stomach or Tiff's, I would scoop it up and swallow it; or if one of them made himself shoot, he would let me lick it off him or even just hand it to me.

We reached the stage where I would sometimes go down on the boys and they would aim it directly into my mouth. I gagged the first couple of times, but I quickly learnt the technique and how to tell when he was close by listening to his breathing and watching his twitches. It made me feel so much more grown-up.

I preferred Jack's taste as it was the sweeter of the two. However, he was also the less enthusiastic one. Steven would be all over my body, especially my breasts, with his hands and mouth, and he would also really try to hit my clit ridge at just the right angle and pressure. His friend, meanwhile, seemed indifferent about finding my sweet spots.

One week, as we were still at the stage of masturbating under our clothes, it was Tiff who finally addressed the issue.

'Look, it's obvious you have some chemistry with Steven you don't have with us. Why don't you both just play together?'

'No no, we're not gay,' they said, almost in unison. 'We like girls. We like playing with you both.'

We gently debated as we gently masturbated. We told them we'd seen the looks they gave each other, but they maintained that before us girls had started coming to Samantha's place, they'd only listened to music and played video games. It was possible, but we thought it unlikely. By inviting us over, it seemed they wanted to convince themselves they were straight.

'It doesn't matter if you're gay or not,' I said many times.

'We don't care,' added Tiff. 'We're not going to tell anyone.'

As if the floodgates were beginning to open, Jack's free hand slowly reached out for Steven's free hand as they continued to self-pleasure. Maybe they were worn down by our argument or maybe they realised we meant what we said.

'We're not gay...' said Jack for the hundredth time.

'We know,' I said, 'you're just "experimental".'

They made that special eye contact I'd seen so many times, even back in the changing room. I'd told Tiff in confidence that it would turn me on to one day watch two males kissing and touching. They weren't yet kissing, but it looked like this was the day my wish could come true.

'Does Samantha know?'

'Of course she doesn't,' said Jack, not breaking eye contact with him.

Without warning, Tiff lifted my top with her free hand and started running her fingertips all over me.

'Woah, what are you doing?' I asked. We both continued to rub ourselves.

'They're having fun. We should as well.'

In fact, they were having lots of fun even though they tried to act cool. It was obvious they were almost in competition to tear each other's clothes off as quickly as possible.

'All right,' I said. I broke my self-pleasure stride and lifted my arms so she could take off my top and feel me properly. My hand then moved right back into my panties to continue the rhythm on my ridge. Her movements didn't compare to Steven's hungry fingers, but it would do for the moment. She stopped playing long enough to take off her own top before continuing her hairbrush handle motion, her jeans open just enough for access.

Us girls then turned to face the boys again to see Jack kissing Steven's neck in pleasure, seemingly by accident, and he withdrew quickly. Forgetting the aim was to hold off, I increased my rubbing pressure. With the floodgates now fully open, Steven went in for a full-mouth kiss, then they added tongues and kept going. I was so turned on I brought myself to the first orgasm of the day, trying to suppress my moans so I didn't distract them.

I felt Tiff removing my bra as I licked the juices off my fingers, and I turned away from her to allow easier access. I then returned the favour and dropped both our bras on the floor. We turned to face each other. Seemingly taking her cue from the boys, I felt her firm nipples touch my breasts as she leaned in to kiss me. When I realised what was happening, I turned to avoid it.

'Why are you pulling away?'

What could I say? She was my best friend and I didn't want to upset her, but there were limits.

'We can touch each other,' I said, 'but just no kissing.' I felt bad because we'd both kissed the boys in our opposite-sex pairs and we both enjoyed it.

After a little discussion, she reluctantly agreed. I did gain a little pleasure from our all-female activity, and at least I had a view of some hot all-male action. But as I watched each one run his hands down the other's bare toned chest with cute nipples and just a little hair, I wished that was me. Before long, they each began rhythmically stroking the other's penis. Judging by their looks of pleasure, they were acutely familiar with what techniques worked for them.

Tiff suggested we try humping each other, this time without underwear as we couldn't make each other pregnant. I was greatly turned on, so I agreed. We found the best way to position ourselves was to sit facing each other and mashing our genitals together. I looked over to see Jack copying us, with his erection pushed against Steven's. But while their parts seemed to 'kiss' in just the right way, ours didn't. It was nice to feel our labia pressed together, and it helped to build my arousal, but there was no way our clits could touch and give us enough stimulation to orgasm from it.

Instead, we pulled back a little and finished each other by hand. What a breath of fresh air after the boys' attempts. Because we both had the same genitals, she only needed minimal instruction to hit my ridge, and I quickly worked out exactly how she likes her hairbrush to be moved inside her. We orgasmed quickly and almost at the same time, Tiff always much louder than I am.

Males, in my experience, come a lot more quietly. I only discovered Jack had done so when he held out his hand in front of me, full of semen. I licked it off, making sure not to spill any on our vaginas, then kissed him on the cheek.

'I wonder what Samantha would make of all this?' Tiff wondered out loud, licking her fingers. 'What is she like? You've never told us much about her.'

'Loud, annoying,' said Jack. He left a long pause.

'What? That's it? That's all you're going to tell us?'

He shrugged, but it seemed we would only need to wait a couple more Fridays to find out.