How do I nicely and professionally reject a coworker?

Anonymous
I started working at this company 2 moths ago, mostly remotely. We are in the same team so we work closely on daily basis. We connected well as friends too and we've seen each other couple of times in the office.
I noticed pretty much from the beginning that he likes me romantically, and I guess I liked that, but I also liked his personality. So we flirted a bit and then he asked me out on a date and I happily accepted. I really was very excited about it all. Date went well and we kissed (we had like a 30 minutes makeout session at my place after drinks in a bar). He couldn't talk after I leaned in and kissed him, he said he was on cloud nine madly in love with me, and it was written all over his face. He kept on saying how I'm perfect and everything that he ever wanted and that he wants to tell everyone about the best date he ever had.
It was too much too soon for me... Sweet, but not the kind of feeling I want (compared to his level). After he left he kept texting me, repeating the same things he said. I told him I like him too but to slow down a bit. It seems he is too infatuated because he's not slowing down he's texting me again this morning with bunch of heart emoticons and all that.
I decided not to continue with this because I don't feel the same. I also have to add that I'm not completely over my ex, which I told him. And I don't want to involve my job in a potential drama, better end it before it got too far. I feel shitty but it is what it is.
Help?
How do I nicely and professionally reject a coworker?
2 Opinion