Should I stay for the kids or follow my heart?

I am married with a great man. He is everything I wanted. Great father and great husband, the only problem is...I'm not in love with him anymore. I am used to him. I tried to rekindle my marriage but it didnt work. I kept thinking about him. 3 mo. ago, I met up with a guy that I went to high school with. In high school, we were completely in different crowds and didnt hook up. But now, we have so many things in common. The only thing is...he is in a rocky relationship and they have a 5 month old baby and I am married with 2 beautiful girls. I want to leave and he says he wants to leave. The feelings I have for him are undescribable and I am sure he feels the same way. He says he is waiting for me to file the papers before he leaves his girlfriend. Should I believe him? Do you think I should stay with my husband for my kids? I know what I am doing is wrong and I know at some point, karma will kick me in my ***. But I cant help how I feel about him. What should I do?