Yes, it sucks. It can be hard to make a wise decision when you want to make a decision based on your feelings.

There is nothing wrong with wanting/asking for exclusivity. If he doesn't want it then you very well might not be a good fit for each other. Don't be pressured into accepting something that you don't want as you may get hurt.

If he says no to exclusivity and you stay with him, and you at some point find out he has been with someone else, how will you take it?

You both probably made a mistake, but that’s young love for ya. Don’t beat yourself up too much about it.