Am I stupid? Advice?

Was with a guy for 6 years (16-22) and had a baby with him at 20. Over our 6 years, he left me a bunch of times and we always got with other people for a few weeks, then got back together. He cheated on me with 3 girls in high school but I forgave him and he was really faithful and good the last 2 years. I always accused him of cheating which is why he left me the final time. A woman from work gave him toys for our baby and I accused him. He left and never looked back. A month later he got with a girl... 20 years old. He's 23. I tried to break them up but it didn't work. 4 months into their relationship, they got engaged. After being together a total of 8 months, they got
Married. Now him, her, and our baby all have his last name. But not me. 6 years and a baby and no ring. Family was against me giving baby his last name but he said I wouldn't regret it and I did. So I tried to get over him and went on some dates and had sex in the back of my car. They didn't talk to me after that. Idk what to do. How can I move on? It's Been a year. I'm desperate. At the last drop off I tried to have sex with him and he refused and got mad and left. How could he cheat on me but not wth me? Why does he love her so much? I hate this stupid girl.