What is this feeling?

I broke up with my ex over a month ago and I found a new guy who is settled, has a job, money, and makes me happy. But everytime I see my ex I get this unexplainable feeling in my chest, I don't understand what it is. I just think he is soo adorable, so loveable, so sweet. I don't think I love him, but this feeling seems like its calling to me wether I want it or not.