Why is he suddenly avoiding me/distancing himself?

A male friend of mine, who I only met about 6 months ago, but have really clicked with, has suddenly become very, i guess, formal with me? Treating me more like an acquaintance than a friend, sticking to the polite greetings and nothing more.

He is very charming and witty and can make me laugh in any situation, and I look forward to seeing him because he is so lovely to talk to. We joke around and he just pokes fun at me, the usual sort of stuff that is really endearing, inside jokes etc. etc.

But recently, within the past fortnight, he is acting more neutral with me. He says hi to me and smiles in the hallways, but never really has these little bits of banter with me anymore and I am really starting to miss our conversations. I asked him if I had upset him and he insisted that I hadn’t.

He is still jokey with all of our other friends, i.e. nothing is depressing him, he is just odd around me and I have tried to engage him in a conversation that is more than just a hello, or goodbye, but to little avail as he gives very succint responses that dont really entail anything else, keeping conversation as short as possible with me. he is not being outrightly rude or anything, as i said he is being ‘neutral’.

This has also made me very nervous around him, trying to keep myself in check, and yesterday he was handing me a book and i sort of couldn’t control my hands lol.. and i grabbed the book weirdly, dropped it almost, grabbed it again and brushed my hand against his finger where he was holding the book and he visibly jerked.
I mean what the hell? He was nice about it though and said “What the bloody hell is up with you today my nickname? haha” and laughed and smiled which was really nice as it was the most I have gotten out of him in a while, but it was extremely uncomfortable for some reason, not like before.

I dont want to keep bugging him as he has already told me he is not pissed off with me about anything, any idea why he might be acting like this? Have you ever done this to any of your friends, if so for what reason?
help meeee :(