Most Helpful Guy
I can't talk for every guy but if the guy wants to be with you enough he'd respect your decision and stick with you, not all guys are like that though for a lot of them it would be a deal breaker. Me personally I wouldn't mind mainly because having someone to snuggle upto and watch films, go walks with, experience life with is enough sex isint a big deal to me.
Most Helpful Girl
If you let him know in the beginning and he stays, he probably won't cheat. Also, at your age it could go either way, teenage boys are immature sometimes and think with one head and not the other, but they may also want to wait until they/you are ready. You're right about it depending on the guy. If it's a mature and respectful person, it won't matter how long they have to wait if they value you and care about you.