What should I do if we do end up working together again?

I was crushing really hard on a coworker, he knew how I felt but when we spoke he never gave me a solid answer. It was a lot or excuses on his part; we work together, we don’t really know each other, he didn’t want me to think he was flirting with me BUT that he thought I was cute and had wanted to hang out with me but felt like I would say no. We agreed to go on a date and than agreed not to. I didn’t feel 100% sold that he wanted to go out with me and asked if it was what he really wanted. He again kept talking about how we work together and how the manager didn’t like him blah blah we agreed to be friend and from then on I made it a priority to see him as just that. His actions toward me still confused me and the dynamic he seemed to create between us was also confusing but I really wanted to keep him in my life as a friend. Flash-forward, I quit my job 4 months ago. On my last day, we went out to dinner, we had a good time and I text him saying so. I also told him not to lose touch, that I was gonna miss him, that now we don’t work together that if he wanted to hang out it wouldn’t be a problem. He basically text back saying he wished me luck, that he would keep in touch from time to time but it seemed very cold. I had assumed we had a good friendly relationship because we texted, spoke at work, teased each other, even after I expressed my feelings. So, in my mind it wouldn’t be an issue if we kept in touch after I left since we were friendly. I thought maybe he was upset I was leaving because he seemed it during my last week. So, I tried to keep in touch with him, I texted him a couple of times and I would send him a meme through dm. The last time I sent him a meme I also asked how he was doing and he that’s when I realized he wanted 0 to do with me. He gave me a 2 word answer and we’ve never spoke again. I’m not going to lie, I felt extremely hurt and used. I figured it’s fine he doesn’t crush on me like I do him but I thought we had a friendship at least.

I just saw him on Tuesday after not seeing him in 4 months. I went to meet up with my friend, that works at the same office as him. I know he knew I was there bc he stepped out and he must’ve seen me sitting with the manager (whom I worked with before and am also close too). My friend saw him sitting in the back after he came back inside and told him i was there, he acted surprised, and my friend told him to say hi. She said he was acting weird, like all uncertain or nervous but she was like whats the big deal?! He did say hi to me but he did seem awkward. I just don’t understand, he’s the one that somewhat ghosted me, why was he nervous or awkward in seeing me again. As I was leaving, I just waved and didn’t even try to make small talk which was my plan originally.

The irony of all this is we might be working together again. But, if that does happen I want to set boundaries, which is what I should’ve done after I expressed how I felt to him. If I do end up going back to my old job, how should I bring up the subject without sounding bitter or hurt. He takes himself too seriously and I don’t want him to think I’m hung up on him still.