Is he flirting or messing with me?

So I have this guy friend from school. We have a lot of cles together and are in chem lab afterschool, so as a consequence we spend a lot of time together (with other people too). Anyway, about 2 weeks ago I started getting the feeling that he was flirting me (i dont like him as any more than a friend btw), and after he overheard me telling one of my girlfriends this I had to come clean and say I wasn't interested in him. He denied that he had ever been seeking a relationship, although things were really awkward for a day. Now, I get the unsettling feeling that he's flirting again. He's always smiling at me and trying to talk, and almost every time I get on the IM i use he sends me a message within 30 min. Sometimes if we're talking via text or IM later in the day he'll end the conversation with "sweet dreams, beautiful", and a little winky face, so I'm not sure if he is flirting or if he's poking fun at our alleged mis-communication of flirtation that happened 2 weeks ago. He's even asked me before, after saying something that seems to have a little bit of a ual innuendo, "would you want to kill me right now if i was actually flirting?" argh its all so confusing, and I cant tell if he's flirting or just joking around (b/c he knows i got super embarred when he found out 2 weeks ago that i thought he was flirting). I also don't want to be a narcissist or anything by thinking he's obsessed with me. Help pleeease!