How do I get courage?

So I am going to be 16 in a few days and the guy I like is 17. He is graduating this year and I have liked him for a whole year. He has been acting like he likes me back, but I still don't know for sure because of how generally nice he is. He treats me differently than his other female friends and i don't know if that is good or bad. He knows that i like him because of a few reasons: i asked him to homecoming (he wanted to but had a family thing), i gave him a valentines card, and because i've talked to him vaguely about it. Last time we talked about it he gave no direct answer or hint as to whether he liked me or not. He just plainly said "You have your whole life ahead of you, don't try to settle down in high school." to which i replied "my grandparents met in high school and have been married for 52 years." he was speechless after that remark, and we were left on awkward terms. He has only had one girlfriend before and that only lasted about a week because she broke up with him. Now that Prom is coming up, there's been a lot of planning done. I am going with him in a group, but he wasn't the one in the group to invite me. How do i get the courage to ask him if we can go as a couple?

If you are too scared to ask him in person try something unique to ask him. Like putting it on his locker with a ton of pictures of you two. That way you won't have to say it, just show him. Or just come right out and ask him face to face. If you don't. You will regret not asking at all.