This can't just be affecting me..

Many times after a relationship has ended for whatever reason (usually relocation) I have come back and end up sleeping with a girl again. This becomes an issue when she has a boyfriend because I can see some self-hate building within her. I've done this with enough ex's that a pattern seems to have arose.

First we'll hang out, have a good time, get it on, and I'll leave for a while. She's left with dealing with the guilt of cheating on her boyfriend. She comes to the conclusion I shouldn't visit because I'd fuck her.

So the conclusion I'm coming to is that fucking ex's that have boyfriends will burn my bridge with the girl. What's your take?