I am a little over a 105 pounds, my boyfriend is almost 140. We are going to have sex for the first time fairly soon. I am a little nervous and would rather be on bottom but he is afraid if he's on top he will hurt me cause he wieghs more and knows he's way bigger/taller than me. He doesnt want to have sex with me if he is going to hurt me (more than the normal for the first time). Is there a way i can prove to him I would be fine on bottom?