Do I have to accept my best friends cheating husband?

It is a difficult situation and no, you do not need to be an enabler to your friend's acceptance of this behavior. Explain that you are HER friend and support her, but you in no way want to be around her husband at the moment. Explain that you saw him schmooze and woo her so many times and that he has a lot of proving to do before you will speak to him. People can change, however you need to wait for a big change. This guy sounds like a real jerk that has your friend going crazy inside. She knows whats going on, she is afraid to leave. I wouldn't tell her to, just be supportive, listen, and refrain from advice. I would listen and then ask her what she plans to do about the situation in place of the advice you normally give. Put it back on her, and just ask questions rather than give answers. If he can go a good 6-8 months being a "good guy" then consider allowing an apology from him to you. Good luck, perhaps he will change, but I doubt it.