Cumming: I need help

My bf and I start dating 9 months ago. He's my first, but I always touch myself alone before I met him(just clit tho, never put finger or anything inside me). When we start doing stuff (having sex) it surprises me that whatever he does, I can't cum. I just can't. I really want to cum while he's inside of me, but I can't. So, every sex session, either I'll just stop when he's done or i'll touch myself alone when he's gone, or he'll try to help like touching my breast, kissing me and other stuff. Then, I will cum.