Cheating

My husband and I have been married a little over two years, we have a handsome two year old together. The other day I found out he cheated on me when we were dating. He was talking to other girls online. He says he doesn't know why he did it and says he hasn't cheated since we've been married. It hurts so bad but I love him so much and I don't want to leave. I don't know if I can ever trust him again. I feel betrayed I know most will say I should leave but if I were to stay and try to work through this, I need advice. I don't wanna give up on us but how can I ever trust him again? When does it stop hurting ? How do I get through this? I feel so alone and I have no one to talk to. I just don't know what to do. Has anyone else stayed after being cheated on? How did you get through it? Do you trust your SO? Do you regret staying?