Why the hell does he regret hooking up with me?!

Last week I went to a party and met this guy named Sam. I was having a smoke and he came over and we started talking. Then his more attractive (but much less interesting) friend waltzed over, and stole the spotlight from him. I hung out with his friend for the rest of the night. I felt kinda bad for Sam, but thought I'd never see him again. I should have known with my luck that I'd bump into him at a different party the next week. We went off and talked for a bit, but my friends all told me that we were talking and cuddling for hours. One of my girlfriends even said later; "He was holding you like his girlfriend! It was so cute. He seemed SO into you!" Eventually the crowds were growing and the music was getting too loud, so I suggested that we go sit someplace quieter to chat. He lead me to his bedroom. While we were going up the stairs I turned around and told him I wouldn't have sex with him because I didn't want things to be weird later and I wasn't like that. Plus, I didn't want him to think I was a tease, so I said straight up, "No sex." We fooled around a bit. He was a complete gentleman, and when I told him he was going too far, he stopped and insisted that it was hard to control himself, but he'd much rather just hold me close to him than me leaving. He also apologized and said he felt bad and never wanted to force me into anything. At one point in the night, one of his friends accidentally walked in on us, but he said not to worry about it. Several times I told him I had to go because my friends would leave without me, and he managed to keep me from leaving him for a long time before I insisted I had to go. He told me to add myself to his Facebook on his blackberry, and took my phone number and called it so I would have his. When I got downstairs, complete strangers kept asking what I did with Sam. I insisted that nothing happened, and then I left. I accepted his friend request two days later and his Facebook status said something about regretting getting drunk the other night for "SEVERAL reasons". I freaked out and deleted him from Facebook. My friend told me to text him instead and ask him what's up. He hasn't replied yet. Do you think he regrets hooking up with me? WHY?! It was his idea, and I warned him I wasn't the type to put out right away. He seemed so sweet and shy before, and the reason why I didn't hook up with him is because I ACTUALLY liked him and wanted to see him again. Do you think he's p*ssed? What should I do? I really liked this guy.