How long after a breakup do you wait to date someone?

There’s a cute guy (28M) who works in my (31F) building who’s been flirting and being super helpful with me for months. About two months ago, we were talking and he revealed to me he was in a very unhappy relationship. Once I found out that he was in a relationship, I made it very clear to him that I would not entertain him. While he never outright did anything along the lines of being inappropriate with me it was obvious he had a crush on me by the way that he would always find ways to start a conversation with me or go out of his way to do helpful things that weren’t part of his job.

About two weeks ago he came to me and told me he had broken up with his girlfriend based off of something that I said to him. This caught me completely off guard and I said loudly “why would you do that?!”. I can tell he was not looking for that reaction and ignored me for a few days.

I felt pretty guilty and reached out to him to check on him. He became very warm and we continued being cordial. Anyway, the other day he randomly texted me from the work phone and said “I forgot to tell you but I got a promotion and will be moving locations.” I immediately went to his office and gave him a big hug and told him I was proud of him since I knew how hard he had been working for it. I gave him my instagram so we can stay in touch and he added me right away but has not messaged me.

I’m super sad he’s leaving and also have a little crush on him. He’s only been broken up with his girlfriend for 2 weeks. Would it be dumb of me to make it clear to him that I have a little crush before he leaves?