Why would he go cold on me?

Me and my co-worker had a good relationship and we got on really well. I started to like him and obviously he picked up on it. We'd walk home together and wait for eachother etc and he'd make up any excuse to get me on the same department as him. Fast forward I got a new job and I had to leave. The day before my last he said he liked me and he knew I liked him and asked for my number. We messaged eachother and everything was going fine.

On my last day at work, we hugged and I felt a shocking feeling (it was so weird) and I cried! So embarrassing but he messaged me when he was done his shift to ask if I was okay and after that he just went cold. I tried to message him but he was giving me short responses. I even jokingly asked if he wanted to ask me out because of something he'd said and he just ignored it. I've left him alone cos I don't want it to seem as if I'm bothering him or clingy. But I am upset I really thought we could at least keep in touch.

Any reasons from a guy's perspective as to why he'd be like this?