UPDATE: He kicked her out of their home b/c he did find out that she was cheating. She has also left behind her child with him. I don't know what is going on with that b/c no one is talking. He's not the child's biological father but he has been raising her for the past few years. It sucks but we're sticking by my bro & the child. It's not her fault her mom is a flake.

That sucks. Sorry to read this. :(

I understand where you're coming from because if my baby sister and her fiance were having problems I'd want to grab him by the throat and be like, "WHAT THE HELL IS GOING ON???"

Just stay out of it, though, and be there for him if he needs you. I say this because if they are having troubles now, you side with him against her, then they get back together, he'll have a hard time forgiving you for going against her.

Does that make any sense whatsoever? It's late and I'm sleepy!