Not really. Do I think about them at other random times? Sure. If I'm having sex with someone, I'm focused on them though. If I'm not even into it enough for that, then what's even the point?
Of course. That's where I think I got my cheating fantasy. My ex girlfriend get sex with a couple guys towards the end if our relationship. She confessed and went into detaul. At first, I was upset, then I masterbated thinking about it for the next month. We had sex afterwards too. I was the other man for a bit. I still think about it, sometimes during sex.