He's always had a special place in my heart

My first boyfriend, I'd consider my first love. We dated for 9 months and split 11 months ago, the circumstances weren't working out on his end so he initiated the idea of breaking up and I confirmed it. The relationship was so innocent, we didn't even kiss until 5 months into the relationship, and we were both fine with that, which surprised me because he was known for moving fast. We didn't even have sex. There was no cheating, feelings of betrayal, or any problems for that matter. The breakup was the first time I'd ever felt anything negative about him. I haven't talked to him since, but he's reached out to me a few times. I never replied.
Basically, I felt I was still in love with him afterwards for the longest time, even now. But I didn't think it was right, I'd started drinking, smoking, going out, making a lot of "guy friends", and I even got a job and started getting my life together. I thought all of that would be enough to feel nothing for him. There were times in my life where I'd feel like I was finally over him, that I was finally free. But sometimes, I'll just be chilling or falling asleep, and it's just, him. I just think about him involuntarily, and I start to miss him, who I was back then, and what could be had I replied.
The thing is, I now have a boyfriend after all this time, and I'm very happy with him. It took him months of assuring me that there's nothing to worry about before I finally said yes to him two weeks ago.
I have a completely new life since my ex, and he's not in it whatsoever. I should feel great, and I do. But sometimes, I just miss him, as a person, the way we were. I don't want to, and I don't know why. please help me..