This is an intense and erotic experience as long as there is mutual passion and respect. Speaking from experience, seeing my partner so turned on with another guy that she had pussy juice running down her inner thighs and her hand stroking his cock before taking it into her mouth was intensely hot. There was the odd pang of jealousy, and I had to remind myself hat she wanted to be with me and this was an excursion that we'd both fantasised about and we than had an awesome threesome. So yes, go for it if you're both up to it and take the time to talk about it before and after.