Help😓

So this guy that I had a thing with about 2 years ago keeps coming back to me and he hurt me real bad in the past he cheated on his gf with me and we had sex (he was my first) I was so heartbroken but 4 months after that he said he didn't mean for it to happen it wasn't his intentions and ever since then he'd always message me and check up on me and his gf and him broke up a while after that I am taken now and he still comes back to me for some reason and I feel bad that I even reply to his texts because I do have a bf and I am happy with him, but I feel like his texts lighten me up and surprise me, but still give me that cheesy smile. He was my first I loved him and probably still do? I'm really confused I'm perfectly fine without him but when he texts me it's like I HAVE to reply because I miss it idk??