i stay out of it unless someone i know and care about is involved. and even then...ill probably stay out of it.
if the boyfreind is a close friend of mine, he'd have known about it before "stuff" happened.
if the chick is a good friend of mine, im going to know she knows what she is doing.
if you are my buddy going after a relative stranger who is dating another relative stranger, ill do anything i can to help you out.
then later call you out as a scoundrel and use your story as an example to my chick as to why im so damn awesome.
edit:
if im friends with all three, im out of it from second one.