Fair Weather Friend

One of my buddies has fallen from my graces recently. I'm not one of those people who has so many friends that I can't keep up with them all. When I send out Christmas cards, I never spend much on stamps. So when you get in the inner circle of Glenn, you're usually there for good. Anyway, My friend Steve has recently been demoted to acquaintance status for me. He has been dating this woman, on and off, for about two years and despite all my, and his other "friends" efforts, he has managed to stay with Psycho-Bitch-From-Hell (PBFH). He's admitted to me several times that he doesn't love PBFH but he keeps going back to her. The problem for me is that he ceases to be my friend when he is with her which makes me feel like he is only using me to keep him entertained during those periods he is broken up with PBFH. Comments? Suggestions?