Like she won

Why do I feel as if my ex mistress won. Maybe it's because that's how she's feeling. My ex and I were together for 9yrs, engaged for about 2yrs and had just had our first baby. I found out my ex was cheating, and I decided to leave. It was hard for me, but I told myself if he were to do it again, that was it. I kept that promise, I hoped he would regret it and ask for us to come back. Instead he stayed with his mistress, who she herself was in a relationship at the time as well. Now they're together, and flaunting their happiness on social media. While I sit here at night, crying, wondering why did he do this to me. To our daughter. Why does he prefer a new family, over my daughter and I. He sees the baby, once or twice a week. And provides her necessities. But I wish we were a family, like we were suppose to be... I feel like she won, and I just let her. Yet he didn't want/love me anymore 😔.