Op, be present in his personal space. See how close he feels comfortable with without overstepping boundaries. Always look yr best, clothes that highlight all your best features,smell nice, appeal to all his senses. I had similar experience as you describe in 2019. I was playing hard to get/long game and not brave enough then to in-act the advice i am giving you now. He did fancy me very much, it was common knowledge, i fancied him too and i rarely fancy in that way.
I went all Anne Boleyn, i dragged it all out, hesitated too much, thought time was on my side, tried to make him work for me ....and then suddenly someone else ( who was married for decades but unhappy ) just put it all out there for him one eve after work and that was the end of that. He still thought i would go with out him and be the "serious" relationship but frankly i was disgusted.
Almost 4 yrs later i am in a similar position and not letting this one go. I have already posted on a similar thread about giving off "vibes" and being more overt, and that's what i have done. Not ashamed to say but : i have got physically close to him and invaded his personal space- he never flinches. Our arms touch, our legs touch,we get physically close, tsot. He is bigger and stronger than me, i am no threat, If he were not happy he could easily bat me away, he does not. I wear clothes that are much more fitted- i see him looking. I lean over when looking at something, knowing that he can see down my top- he looks when he thinks i cannot see him. I always top up my perfume and make up before i know i will see him and he always says i smell nice. I wear the same one perfume at work , he associates that smell with me now, can literally see him inhaling me when i am near him. Basically, i am not hanging around anymore. This has been over a 5 week period but i have known him longer. I am making it obvious and he has certainly picked up on it. He sought me out, way offsite, on the last day of term 1:1. Based on my own thread, i am going to see what Nov and Dec bring. We will have multiple opportunities to be out socially so, if it does not happen then , it never will. As we work together i will likely make a decision over xmas holidays if it is going no where. I won't waste time anymore after that and will move on .