How do you know if a guy wants a future with you?

I'm not so sure right now if my boyfriend really wants a future with me... It hurts but I'm so scared to bring it up in a conversation. Some of the stuff he says to me, makes me feel like he just isn't sure if really wants to marry me. We're both 18. I know, I know I'm "too young" but still. I love him so much and I feel like he really does too but sometimes it just seems that way. I don't want to lose him. How do you guys know if a guy wants to marry you or have a future with you? Is there even a way to tell?