Breakup issue. Things. i am just sad.

Hi, I was in a relationship for almost 5 years. And recently something bad happened. I unconsciously slept with someone else. It all happened out of my consent, I didn't want my relationship to end hence I told everything to my bf. He broke up after that. But we are still in touch, moreover we kept meeting, he also had physical intimacy with me, but when it comes to marriage and future, he denies and now he says he needs to breakup. Wants me to stay away. But he keeps messaging, and talks very normally, he says he wants to meet me and talk to me but won't marry me. It is very difficult for me handle these things now. I am finding it very difficult to handle the pain. I feel I am weak, I don't mingle with any other person now, I don't feel like talking to anyone. I need help. I keep thinking about all the things we used to do. I feel guilty for things. I am just sad.