<human>: I have a friend who has been dating a girl for about a year. Before they started dating, I was friends with both of them, and I was happy for them.
 It has become apparent, however, that he doesn't really seem to care about the relationship. He cheated on her 6 months ago (she still doesn't know), was going to break up with her to hook up with one of his female friends before deciding against it, and is generally not open with her. 
I have become frustrated at this because I really do like this girl. We have a similar sense of humor, she's pretty, and there are a lot of little things about her I like. She also tends to act somewhat flirty with me, which makes it worse. 
What do I do? Wait until they break up? Any advice is appreciated.

Give me the gist of the text in a nutshell
<bot>: I'm attracted to my friend's girlfriend. He's not a good boyfriend and I don't know what to do.