I agree with you wholeheartedly, especially as his fling seems to be spilling into your home gradually. It's true that whatever he does on his own time is his business, but now that his new gf is calling the home, I'm sorry, that would be too much for me. You don't just "downgrade" from married to roommates in 3 months. I wonder how he would feel if you had a new beau and he started calling you at home, texting you repeatedly and writing little messages on your Facebook page...I'd bet he'd be all up in arms about it.
So yah, I agree with your decision. It's your home and you deserve a safe place to rest your head.