In love with current relationship but sometimes think about my ex.

I 28F am in love with my 29M boyfriend who I want to marry and have kids with. He makes me really happy and treats me amazing & I see how he’s going to be a great father one day and I can’t wait to start a family with him as we’ve gotten to that point & are talking about marriage and kids. However, I’ve been dating him for almost 2 years now & I don’t know why but I occasionally still think about my ex. I would never go back to my ex, but when I do think about him I think about the sex and connection we used to have. I’m not saying my current boyfriend and I don’t have great sex, but I feel like it’s different than my ex, maybe more passion? I really don’t know. The reason my ex and I didn’t work out wasn’t because he wasn’t a good guy, but our relationship had some pretty bad downs toward the end of it, nothing abusive physically, but mentally exhausting and draining & never knowing if we were gonna work out towards the end. We both made some bad decisions both of us before we started dating which affected our relationship the whole time, but we tried to look past it because we did love each other. There were so many highs and downs during the almost 2 years we were together. Now that I’m almost 2 years into my relationship with my current boyfriend & looking towards building a real future which I do want, I tend to think of my ex a little more. I don’t want him, I wish him happiness and hope he lives a great life with whoever he chooses to be with. Is there a reason I keep thinking of him? Is this normal? How can I look past this? I don’t want to ruin what I have going on currently because I see the whole future with my now boyfriend.