I don't want to put my head in the grinder and offend any of the few female posters we have here, but in my experience, women and men look at sex differently. For the most part anyways. Normally, to a man, sex can be completely divided from any other feelings of attachment. There may be momentary feelings of competition, but normally not outright jealous anger. Of course, as a straight man, I've never had a male partner, so I can't comment on that exactly except for my own encounters with women and accounts from friends. I normally didn't hook up with girls that were taken, just because it wasn't worth the inevitable drama in my opinion. But there were several occassions when I came to find out they were taken. Even though it was agreed before hand that neither of us wanted something serious, they always, ALWAYS flipped out once they saw me with someone else. I even had a girl curse me out at a local bar when she saw me, and she was there with her current bf! He wasn't close enough to hear obviously, but the fact that she was angry enough to risk spoke to how jealous she was. (or how crazy!)
If you are going to regularly sleep with women that are taken, then you should just get used to the fact that no matter what they say, emotional connection are going to be made.