Why is my guy friend acting so moody?

I have been friends with a guy I work closely with for a year. At some point in the year I realized that I liked him as more than a friend but tried not to show it as I didn't want to ruin our friendship. I started to think that he felt the same as he started to lean against me and touch me with any excuse - he is very shy and doesn't normally behave like that. He also seemed to be jealous and moody when I spoke to other guys. Our friendship really peaked and we were hanging around together almost all of the time. We going out one night and I decided to say something. Towards the end of the night he seemed scared that something might happen between us and really kept his distance. I was confused by this and just came out with it all. He was really spooked and said that he had never liked me that way. Then at the end he told me he was seeing someone else but didn't know whether to tell me that or not. I found out that this was true and he had been with someone for a month but hadn't told me before. I decided to put this down to experience though of course I was upset. He seems happy and I am pleased for him.

However, now our friendship has become very weird. Whenever we start getting on as we always did in old times he suddenly becomes moody and distant. I never push this - he seems to really want to go back to being friends and as soon as we start having a laugh or whatever he suddenly changes. This is really upsetting me as I feel I have lost a friend. Why is he behaving like this?
Why is my guy friend acting so moody?
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