Why is he acting like I did him something?

So long story short, I had a guy at work that liked me, that was very flirty with me sexually right? We have a huge age difference between us so I could never date him, have fun yes. We never did anything just sext that’s it. Well before we talked outside of work, we used to play and laugh with each other. He was flirty he would make sexual innuendo jokes all of that. Well I ended up telling him that I couldn’t do anything with him because I have a situationship going on with another guy and I felt like I owed that guy more loyalty. We aren’t together but he would want anything to do with me if he knew I slept with another guy. So the coworker accepted that from what I could tell and things were still good between us, he would still crack jokes on me. Then out of nowhere he started acting different, I’d go up to him just to make causal conversation and he’d act like I was bothering him or talk to me very dryly just not be himself around me. I asked him at least twice or point out that he was treating me different from everyone else, he never addressed but pretty much said we didn’t have to talk to each other and that we could do a simple greeting and then we go on about our day and then he unadded me. He also said that he shouldn’t have made me feel like we messed with each other like that, I mean this all started from his end not mine so that’s a gaslighting statement. Before that there was a girl on his story like she was recording both of them. I wasn’t upset about that because I never wanted to be with him, it was just on wanting sex and being lustful for me. So he now has a girlfriend, so I guess he was trying to sleep with me but was talking to someone else not sure. So I don't know if that’s why he switched up, I mean we don’t have to be flirty to interact with each other but he treats me like I did him something. So does anyone specially guys have any insight to why he’s treating me like that? I’m not heartbroken because my feelings weren’t attached.
Why is he acting like I did him something?
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