Depends on whether I think the boyfriend's right for her. I know I shouldn't be the one to decide, but thats the way it works for me.
This guy is just fantastic. There's no way you can dislike him.
And altough she's incredible, she really is, I think it would be a pretty selfish thing of me to mess around with her when she's happy with her boyfriend. I'm not sure if she'll be happy with me in the long term and I think that guy deserves her just as much as I do.
The only thing I must add is that I'm the one to decide how far I go with her.
I don't mind her lying in bed with me or hugging me. And I don't care if he's allright with that. I just won't have sex with her. Which, and I know, I've been in this situation before, is incredibly hard. But because I respect her so much, I think I can be strong.
Edit: I don't think she'll make a pass on me, I do think things can 'happen', even altough neither of you really 'starts' something. That's the time to be strong