I want to have sex with my boyfriend but..?

I think you should wait a bit longer. Until you deem it right that you have no question in your head that you do not want to do this. I am 18 also I know your predicament well. Just wait and be sure that you want to lose it too him. No second guessing because if you have that then your not really ready. Just wait longer ,and he will be happy you did because well you were ready and sex kind of changes the relationship a bit.