Advice

There is a guy that I talked to a few years ago and we talked every single day for a few months. I knew I shouldn't have, but I fell for him hard and fast. We talked about everything and I thought that we could end up together forever, then all of a sudden this girl comes along and they very quickly started dating. At that point she had been with every guy that we worked with so it made no sense that he would want to be with her over me. He ghosted me and I finally decided it was time to move on and get over him. I left the job that we worked at together and have been gone for almost a year, now I have to go back to the job due to some unfortunate circumstances. I haven't seen him since August, but I still have feelings for him. I still think about him constantly even though I keep telling myself to just get over him. I just don't want to see him everyday again and get hurt again. Does anyone have any advice on what I should do? Should I avoid them altogether, should I be friendly with them? Anything helps at this point. I also should point out that when I was still working there I would catch him staring at me all the time. Even other co workers started to notice how he was looking at me and I believe he had strong feelings for me at some point.