What do I say to my cheating friend?

We have been friends for going on 3 years now. A while after becoming friends she confided in me that she'd been having an affair for about 2 years. She has been with her husband for 10 or 11 years and they have 4 children together. Trying to be a friend I just listened and all that trying to not judge. But now the affair is going on 5 years and I just can't take it anymore. I am not trying to judge her I just feel in my heart that what she is doing is wrong and I can't support it. I have tried to talk to her and she has never became angry with me, I have told her things like maybe if she took all the energy she puts in her affair and puts it in her marriage she can be happy again with her husband. When she tells me things her "boyfriend" does I have no response, if she thinks it's funny, I don't laugh with her, if she is hurt, I don't feel with her. She asked my opinion and I told her she can't ask me because I'm bias, she says I shouldn't be and I told her I am because I think she should end things with him and focus on her family so no matter what the guy does I am never going to think awww what a great guy, it's just not going to happen! So, tell me, how would you handle this?