40s F struggling to understand guy's reaction after after date - looking for insight

A bit about me. Early 40s, never married. Out of the dating pool for a very long time. Was caregiving for a family member. It was brutal and emotionally devastating.

Following their death late last year I was able to move back to the city and work in the office finally. Huge corporate environment. Have a very technical job.

It was nice to get some semblance of a life back. Got in shape, started getting lots of attention from men but didn't think much of it. Again, was just trying to get my life back.

Immediately meet a guy my age at work. Different department, very little interaction with them. Don't see him every day.

Pretty quickly picked up on interest. Guy was showing up everywhere. Always making contact, starting conversation. Figured he was just being nice as he does have that reputation. I don't talk much at the office (on the shy side) and mind my own business for the most part so didn't really engage.

After months and months of this I started to realize it wasn't a coincidence. He would act very nervous and a bit strange. Very intense, but respectful/polite. Would remember details of past conversations. I started to become attracted.

Finally initiated contact when I ran into him alone. He asked me out after a few minutes which surprised me (he didn't know I was single). Dude looked terrified.

We go out and I was immediately... surprised. I thought it was just drinks. He said he hadn't been on a date in years following a divorce, that he had been attracted to me immediately and had dreamed of this moment. Was nervous as heck to the point of convulsing. Asked me tons of questions about myself, took notes on my interests. Was very open about his background, warts and all. Said I was stunning and intriguing.

We laughed, talked for hours, went for a walk, ended up someplace else where the conversation continued. I was friendly but reserved. In my head I thought "this guy is so into me and can't wait for the next date."

Here's where it all goes wrong. We were about to part ways and I walk up to him and kiss him. I can't explain it. I've never made a move on a guy like that before.

He went crazy, I went crazy. Went home with him. Awful decision as I really wanted to get to know him first. But I did what I did.

Things got awkward quick. No contact the next day. Then he started approaching me in the office and staring and smiling intensely. People were always around so I would just say hi and walk away as I was nervous and uncomfortable with my actions. Also, he does have my # but never contacted me on it which upset me. So I figured he got what he wanted and that was it.

But weeks went by and it was the same. Initiating contact in the office, staring and grinning and eventually I could sense confusion as I wasn't really responding much and I could tell from his body language that he was frustrated.

So I eventually ask him out for drinks. Explained that I was partially ignoring him bc I was uncomfortable with myself and that I just wanted things to not be awkward. He was quiet at first but the conversation flowed. Eventually admits that he thought I ghosted him. Said he can't contact me bc he only has a work phone. I find this EXTREMELY suspicious. I know for sure he does not have a girlfriend and based on his behavior I could tell he hasn't been w/ a woman in years.

We spent hours chatting and he was acting extremely nervous. Staring and smiling. Remembered every detail from our date, every conversation. It got to the point where even the bartender asked me if he always acts like this around me.

So what could be explaining this kind of behavior? I'm struggling to comprehend this.