i recently found myself in a similar situation with my lover asking advice about his relationship with his long term girlfriend. I felt challenged and uncomfortable providing any advice that wasn't supportive of his relationship as worried about not being unbiased. I went away and reflected on my motives and realised i did have love and integrity at the core of my intent of giving advice. I considered that if he was a friend without being a lover i wouldn't be worried about giving my opinion if asked, and i decided that as friendship and honesty is the basis of our relationship then i owe it to him to be honest and give him my opinion, as he wanted it. I don't however, plan to make a habit of this, because as much as i want to support my love and this includes being there to help him work through life stuff (such as relationships with others) i think ultimatly they must and will, make decisions based on what THEY feel is best, not on the projections of others. I think from now on, i will listen if needed, but hold back my opinions and just support them to work with what THEY know. So my advice is to let your girlfriend know you are there to support her, but also explain to her that its hard for you to provide advice as you have a conflict as your friends with her girlfriend and to encourage her to make whatever decision is right for her and reassure her that she will be supported no matter what she decides, or doesn't decide. I think its great you are acknowledging your conflict. And you certaining don't sound like a homewrecker. You are only responsible for your relationships and friendships and your actions and you know when you are acting with integrity. Whether their relationship continues or ends- that is THEIR responsibility and because of THEM not you. Let them own the responsibility and just trust in yourself and know that as long as you are holding love in your heart-you are doing the right thing.