What happened between me and this guy?

About 6 wks ago, I found out the cute guy (who's 3 yrs younger than me) that I would sometimes see at work lived a few blocks from me. We ended up sharing a taxi and took the train to work together. We seemed to hit it off and swapped numbers with plans of hanging out after I took the bar exam...ALL his idea.

We texted here and there and hung out twice. The 1st time we hung out, we sat on his steps for a few hrs and talked. Also, we had our 1st kiss. The 2nd time, we talked a lot, and he performed oral sex on me. Because he didn't try to have sex with me and was all about pleasing me, I assumed (maybe incorrectly) that he really liked me. I also assumed this because he would often talk about being in my life in the future, things he wanted to do with me, and treating me like his Queen.

Monday through Friday of last week everything appeared fine. He hit me up everyday that week, and we even FaceTimed for the 1st time. I didn't hear from him at all until I bumped into him 5 days later at the elevator. He held it open for me, and we exchanged "good morning" greetings. That was it. The next day (today) he saw me getting tea, and he didn't speak at all. It was if he didn't even know me. He just kept talking to one of our colleagues.

FYI- he's informed me, whether correctly or not, that he wasn't in a relationship, and that of his knowing none of the females at work was interested in him like that.

I'm just really baffled on what could have happened. Any suggestions?