Very hurt and confused about a close friend’s sudden behaviour

I met J four years ago at work. We work in the same building with different companies. I kind of guessed he was attracted to me by the way he acted but he never said anything until about three years ago when we went out for drinks together. I’m wasn’t in the right frame of mind at that time, so I told him no. We did become good and close friends and he confided a lot of things to me and we went out for drinks and clubbing sometimes, and hung out a lot after work. He called me his best friend and a good influence in his life. Recently he started dating, but he hid it from me for a what I think was a long time (I have no idea when they started). I heard about it from another mutual friend who heard from another mutual friend. I asked him about it and although he didn’t yes, he didn’t deny it either. Fast forward a few days, I got quite pissed off with his hedging and he finally said yes. So I told him that being the supposedly close friends that we were, that nothing explains why I had to hear it from someone else that wasn’t even close to any of us. He said well I should know him by now and that he adopts a separation of work and private life, and that he’s kept that quiet because she also works in the same place. Well, I apparently didn’t get the memo. I don’t think he has ever had that separation with me, he tells me a lot about everything, and he knows I never gossip about him. Am I an idiot to think that he should have told me about it, and not let me hear about it from others, and not continue to lie to me about it when I asked? I never had a problem with him getting a gf, I’ve even offered to set up his tinder for him. I felt like a fool for not knowing and had asked him out for drinks, movies, and out to club. And being blindsided by the sudden whole separation of work and private life thing. I have provided him with support from day one of him opening his new company, given him gifts for every birthday (I’ve never gotten anything back), listen to him complain, etc. I told him ok, but he’s still texting me asking how I am, if I’m feeling well because I was cold to him, and trying to share funny videos. I don’t know what happened. I don’t know what to do. I don’t know what to say. And frankly I’m quite hurt. What should I do?