Why must people annoy me?

Ok so I love my friends but why must they think I am their therapist. I've been friends with my one friend for years. She bitches and complains about stuff but causes most of the problems she bitches about. She was with her BF for about 3 years but cheated on him most of the time they were together. Now in her somewhat defense he constantly accused her of cheating so she did it. I am just so tired of her bitching about it. It's just annoying when you hear the same ol' shit every single day. I just wish she would resolve this shit already or just grow up. Just get the fuck over it and move on or shut up about it. But she's been my friend for so long so I'll just continue to pretend to listen and pretend to care about it.