I [22F] ended my relationship with my boyfriend [25M]. Did he develop feelings for another girl, or was I overthinking it?

Hi. I recently broke up with my boyfriend, and I would really like to hear an outside perspective because I can’t tell anymore which of my concerns were reasonable and which ones may have been caused by overthinking.
We met at work. At first, he seemed almost perfect to me. We talked a lot, he told me many things about himself, and I genuinely thought he was exactly the type of person I had been looking for.
But the deeper I got into the relationship and the more I learned about him, the more confused I became.
Early on, he told me that shortly before we got together he had been seeing a girl in another city without having serious feelings for her. He also told me about intimate fantasies they had discussed. What confused me was that only about two weeks after being intimate with her, he told me he had fallen in love with me.
I couldn’t understand how someone could emotionally switch so quickly. Maybe that’s completely possible, but it was one of the first things that made me question how he viewed love, intimacy and relationships.
As time went on, other things started bothering me. He sometimes smoked weed and played poker, and I gradually realized that some of his choices and values were very different from mine. None of these things alone necessarily made him a bad person, but I started feeling like the person I was getting to know was different from the person I thought I had met in the beginning.
Then our communication changed. He stopped telling me much about his day. He would say things like, “I’m going to sleep” or “I’m resting.” At the same time, I could see that he was capable of communicating much more openly with other people about work and what he was doing.
I started asking him for more attention and emotional support. When I tried to explain how I felt, his responses were usually things like, “You’re tired,” “You need to rest,” or “You’re overthinking.” I didn’t need him to tell me why I was feeling something. I wanted him to actually listen and talk it through with me.
Then there was another girl at our workplace. She was attractive, and I started noticing what seemed to me like a change in his expression when he looked at her. It felt like his eyes lit up around her. I know this is subjective, so I don’t want to claim that this proves anything.
Later she was promoted, and he started messaging her frequently about work. Sometimes they joked with each other. I never saw anything clearly romantic or inappropriate, but what bothered me was that there were other people he could contact about some of these work matters, yet he seemed to choose her very often.
I told him that this made me uncomfortable. He said I was imagining things.
Toward the end of our relationship, I noticed that he was still very active in communicating with her about work. It started feeling as though he was looking for reasons to message her. Again, I don’t know whether that feeling was accurate or whether my trust had already deteriorated so much that I interpreted everything negatively.
Another thing that damaged my trust was his habit of deleting messages. With everything else going on, that made me even more uncomfortable.
I kept trying to explain what was hurting me, but I felt unheard. One of our last conversations really stayed with me. We were driving together, stopped to get something to eat, and I explained again what was bothering me and how I felt. Afterwards, he didn’t really try to discuss it with me, ask questions, reassure me, or suggest that we work through it together.
Eventually I reached a point where I couldn’t continue the relationship, and we broke up.
Now I’m left wondering: from an outside perspective, does his behavior toward this coworker sound like he may have developed a crush on her, or was it normal workplace communication that I interpreted differently because I had already lost trust in him?
And even if nothing was happening with her, were my concerns about the relationship itself reasonable, or was I genuinely overthinking too much?