If you're having doubts about having sex, then chances are it might be a bit too early for you to engage in that activity. You need to make sure that you are emotionally prepared for it, sex isn't just two people "doing it", there's a lot of emotion behind it as well. You said you're worried it might ruin your relationship...bring this up with your boyfriend. If you choose to have sex with him, explain to him your thoughts and worries. And if you choose not to, express your thoughts and worries as well. Communication is key in relationships. You said you were worried about getting pregnant...Make sure he's the kind of guy who'll stick by your side if you did get pregnant.
Good luck, I hope this helps! And feel free to message me with any other questions
I noticed we're both 15 :3