Feeling weak and regret

My boyfriend cheated on me 3 weeks ago..he is still in my social circle so I still see him. Obviously I broke up with him when I found this out. I had been missing him a lot lately and I just wanted to get closure about our relationship. So I went to his house (stupid on my part I know) to talk and I ended up crying and he was comforting me and one thing lead to another and we hooked up. I feel just so weak and humiliated I would do that to my self. We promised to never talk again after this but I just can't forgive myself