Best way to cope & know if i am getting mixed signals?

Long story short. Meet my ex over 5 years ago. We were engaged to be married and I found out he was talking to a girl from the internet. Of course caused problems. But they were just "friends". Well eventually that took a toll on our relationship and I took a huge step and moved out of our house and got my own. He still came over and did everything just like a family would. Because I have an 11 yr old son that he was dad too. Well the day before Thanksgiving this year... His Married girlfriend and 4 children moved in with him. Totally ripping me apart. But he said he still want to be friends with me. Well after 3 weeks she left him. And who does he call me. We talked and he promised that he wouldnt let anyone come between us again and that I wouldnt lose him and we would work on things. Well after 3 weeks of happy bliss... she is back but without her kids. And I am mortified. Because i put more of myself in the relationship in 3 weeks then I did in the 5 years. How do i cope with this?