I still miss my ex????

I just started dating a new guy but I’ve realized I still have feeling for this guy was with before I got in the relationship. We weren’t together but we had moments were it felt like we were and it kinda caused me to fall for him. I don’t wanna mess up my relationship for someone who might not want to date me but my feelings are distracting…

What should I do?

Update: I always feel happy around him. He’ll contact me every few days to check on me and see if I wanted to hang out. I started to want a relationship when I felt a shift in how he was with me after I told him I had feelings for him. He seemed more attentive and fixed a problem when he noticed something was up.