I can't tell if he likes me?

I've known this guy for 6 years, since high school. (we're both 23 now) During all this time we never once spoke to each other until the end of last year when i was dating his roommate at the time. From that time on he started talking to me more, and just being super nice to me.

Recently, within the past few weeks he would come up and say hi to me and offer me rides home. He'd tease me, or act like he was going to hit me then doesn't. He'd ask me questions that i knew one of his other friends could answer for him.

He asked me if i'd like to watch the new season of big bang theory when it comes out on dvd with him. But the plans are kind of just floating around in space with no day or time attached to them. Should i ask him about it? or wait and see if he says something?

Though, what i find weird about this is it's like some days he's super flirty and, others we hardly speak to each other and it makes me feel like i did something wrong. Is this normal? Or should i try and be more responsive to his flirting?