I'm tired of my tighting during help!?

I love my fiance and I love having with him. Ive been with him for 6 years and i'm very happy. But when we have im tight at the begining which is fine and he likes but when we have for a long time like even just for a half hour if he pulls out for even just a second and tries to push back in i'm tight again. hes always able to get in and it doesn't hurt me but after awhile like if we have for and hour it starts to hurt him. He never complains and he is always trying to see if he can help the problem like lubricant and everything. but i feel bad i don't mean to be that way and i want it to stop. it never hurts to have i just want to be able to have sex with out it being so hard for him to . is there anything i can do to fix the problem becuase i love having sex with him and i want to make having long sex not hurt him in the end.