My life is falling apart

I'm 25 and I have been with my husband for 6 years. We got married 2 years ago, when our son was a couple of months old. I have always felt like I have to fight for his love. He yells at me all the time, and some times pushs me around. He can never hold a job. He has a part time job now and only makes enough money to pay his bike and truck. I have to worry all the time about how things get paid. Last summer he almost cheated on me. Im not sure if he did or not, but pretty sure.At the time I was pregant and lost the baby. After that my life changed. I started not caring for him the way I use to. And start living life for me hanging out with friends. I did alot of things I'm not proud of. But you have to see I was so comment to my husband for years. He was the first guy I have ever been with. Anyway one of his friends came up and we kinda fooled around. I no this sounds bad I was so hurt. We both didn't want anything out of it at first . Now its growen into some thing I have never felt before love. I work out of town and come home 3 days a week to my husband. we haven't slept together in a long time I sleep down stairs. But his friend and I are together all the time. I no I should leave my husband but I'm having a hard time leting go I don't no why. I don't want to hurt my son but staying with him will. I don't want my son to grow up treating women like shit. And I don't want to lose this other guy. I'm kinda worried that this other guy might cheat on me. I no he loves me but he has cheated on other girl friends. He had a girl friend at the time. Of 2 years I hope this doesn't sound bad on me. I don't no how it all happened. I'm so lost I feel like I'm going to lose it. I'm so sad and feel very stress. What should I do???