How to know if he's curious/questioning?

Hi everybody. So I've recently gotten to know this guy who I wasn't sure about his sexuality at first, but apparently he does identify as straight. I was talking to my friend about him, and I was telling her that I liked him, but it was hopeless. She asked if I thought there was any chance, and I said I doubt it, and then I joked about "straight" guys liking me before. He was nearby and I know he was listening. Then my friend (she's very forward) asked him if he was gay, or bisexual. It was kind of weird, he wasn't offended or anything like that. He seemed sort of reserved about the whole thing being honest. He eventually said that he wasn't. Then she went further by asking him if he thought I was attractive. He did a little chuckle and said he wasn't gay. We eventually said we were just kidding about the whole thing. Since then, it's been a little weird between us. Not like bad weird necessarily. He still talks to me and is nice. But it just seems like that conversation is on his mind every time we're alone together. I even seem him looking at me sometimes. I just don't know to what extent it's on his mind. Whether positive or negative. What do you think? Any advice?