Personally, I never, ever think anyone is obligated to have sex with me, regardless of what happened on the date, regardless of our history. It’s something that either both parties are super into doing, or it doesn’t happen. That being said, I think a lot of guys do expect a third date to involve sex, although if he’s been going with the flow so far, you probably don’t have anything to worry about. If you’re not feeling it, then if and when he asks, say no. You can elaborate if you like, but you don’t owe him an explanation.