31 + 2 wks pregnant and cheating fiance

So I forgave him a couple times before the first time was around the time I got pregnant I found 52, yes 52! Women he was messanging on FB. His excuse "He didn't think we were serious." Yet we had already decided to have a baby together. The second time I made him leave because we needed time apart I was 2-3 months pregnant and he was gone an hr and messaged some other female inviting her over. Now last night he messaged some female saying he wished he could be with her. This time the excuse was he can't put up with my family not liking him anymore to some it up. But denies it happened last night and who with when I have freaking proof. This after he told me to take my ring off and take it off FB that we are engaged cause I told him I wouldn't stick around if he went to jail because he was talking about fighting some dude at work. He says sorry but he's only sorry he got caught. Lets not forget it shows he messaged 3 other women but those messages are gone. Why am I having such a hard time just making him leave? My children deserve a better role model, I deserve better! And he does this knowing I divorced my ex husband for cheating. How can he treat this as no big deal?!?!?