One Lonely Degree is a book about this situation (among other things). A few of the write-ups I've read on the book have been angry with Finn for not always doing what they consider the right thing in this situation and some people have suggested that in making Audrey such a good friend Finn becomes unsympathetic. Some of these folks would give Finn more leeway if she wasn't crossing a line against someone who is genuinely a loyal friend, but I've always believed One Lonely Degree was a story about good friends, to make it otherwise would be too easy.
People are complicated. Even the ones you like a lot aren't always going to do what you consider to be the right thing. And I think many of us, when put in difficult situations (like Finn is during One Lonely Degree) could do things that we ourselves may not feel comfortable with. But we still might do them.