I feel betrayed by my family. What do you think?

He was going to her for 3 to 5 times a week. Does any more need to be said? Your family obviously side with him, is there good reason, I guess he wasn't getting any at home, or he wouldn't have had to stray. He is a bit of a rat, for doing it with your friends, which I guess is what's hurting you the most. BUT, there has to be a reason for a man to go doing this, and you have to look to yourself to find the answer. Business or no business, you two need to part company, and quick, otherwise you will never be happy.