Why am I thinking about my ex?

Ok so I’m 16, and a few months ago I had my first boyfriend. Like ever. I’ve never even had one of those fake middle school boyfriends. He was really nice, but super awkward and tbh I never really had that good of a time with him. It was never a bad time, but just nothing super fun ever. He reeeaaallly liked me and I told myself and him that I liked him a lot too. We knew each other about two months and dated about one month. I finally broke it off because I felt NO emotional attachment. Like I was constantly making up excuses not to hang out, he always texted first, stuff like that. I was not the least bit sad when we broke up, although I did feel kinda bad for him bc he was really invested in our relationship. Anyways, three months later and I think about him literally every day. Like there has not been one single day I haven’t thought of him. Sometimes I think of how glad I am that I’m not dating him, and sometimes I think about what would happen if we were still together. Idk. I don’t know why I can’t stop thinking about him three months after I broke up with HIM. I’m so confused.