Yeah. Some stuff I have to say about this is that:
- This is a very messy situation so it's best NOT to get involved
- You never know, she MIGHT be lying about how he's treating her
- Regardless, you can find someone better! Just keep looking, and I'm sure you can find a very nice partner. Don't settle for anything less than you deserve. If she's cheating on him, she might cheat on you in the future, so if I were in your situation, I'd try not to get involved.
Hope this helps, even if only a little bit!