Past boyfriend coming around

I fell hard for this guy named Seth. We were only together a little over a month last year. He was so sweet and kind. A gentleman. He opened doors, pulled out my chair. I couldn’t drive at the time because I didn’t have a car (but where I live I can walk everywhere). So he always offered to come get me.

One day on the phone he got super quiet and said he had to be honest with me. Before me he was in a long committed relationship. I knew that. He said that he thought he might still be in love with her. He didn’t think it was fair to me. After we got off the phone, I cried. You know the usual stuff. Damn hormones.

6 months later, he started calling me again. It was nice talking to him. I don’t know why he did though. I was talking to him and this guy I just started seeing, James. James and I weren’t exclusive yet because we were just talking. Seth called the other day and asked if I wanted to get together again. I told him I was kind of see someone else now. I felt bad about it that day but now I’m in that period of “where were you 6 months ago?!”

Why break up with me and then start coming back around. That’s not fair to my emotions.

To add: I didn’t go running to someone else. It just happened. I didn’t date anyone else the 6 months after we broke up and it took me that time to not be hurt by it. His emotions do matter but I’m just confused by what’s going on in his head.