Well the good thing is, your young, and your hormones are out of control x3 (its okay mine did that too at 15). But i say ask him out, it will be fun (hopefully) and also you might be having this problem because you just havn't found a person that you care for yet.
Well if you don't want a relationship don't enter one. If you do enter a relationship, take things slow. You do not have to cuddle or any of the other love dovey stuff what so ever. A relationship can be whatever you want to be. You guys could be best friends that kiss and stuff and leave it that way. You can also just be friends with benefits with him, not strings attached just sex.
Then don't have a relationship. Make sure the other person knows that you don't want a relationship, create rules/boundaries (are you going to be sleeping with other people etc) and take precautions to ensure you don't end up pregnant or with stds.