I’m in a long-term relationship, but someone from my past messaged me… and it’s thrown me off more than I expected

I (25M) just got a message from someone (24f) I was with years ago. We dated young and were together for a year, we were even friends before. I was in love with her we broke up after a year of being together. She was in a complicated place mentally and emotionally, and going off to college. At the time of breaking up I thought she was the woman of my dreams, but not the relationship I wanted. She was never the lovey dovey kind of person, and I though I needed that. Eventually I tried to get back together with her, but she didn’t think it was a good idea. We stayed friends for a while, but it was complicated. Eventually we lost touch. Except we never really lost touch. We’ve always had this… thread. We’d go months, years even, without speaking, then randomly fall back into contact like no time had passed.

A few years ago we started talking a lot again I mean daily texts, late night conversations, checking in on each other. I didn’t know what I was doing. I had a girlfriend. I still do. But I wasn’t in a great place with my gf and talking to my ex felt like no time had passed. It got to the point I was taking to my ex more than my gf and I didn’t know what to do. I thought about breaking up with my gf. But I didn’t. I stayed. As we continued to get closer (although I will say we were just talking, not meeting up or anything) my ex said it wasn’t right and pulled away. She was probably right.

A couple years went by. Total silence aside from random meme or checking in text. Then she messaged me last week. Nothing dramatic. Just said she’d thought of me and hoped I was well. I replied politely. She asked how I was, told me a bit about herself. We’re talking again, a little.

I’m all messed up.

I love my girlfriend. And yet… I think part of me is still 18 and heartbroken.

I don’t even know what I want from this post. Advice? Reflection? Validation?