Cervix and Sex question help!!?

Pan
My boyfriend really wants to go deep, I really want to let him. He's a tad big and still has a few inches he can fit in. It hurts when we try, a lot. Is it because we haven't gone that deep, maybe it's not my cervix, just something my body needs to take getting used to?  If I let him go all the way in, will the pain eventually stop? Will it damage anything?