Unprotected IUD sex (all the time)

Okay so me and my fiance always have unprotected sex. We have used two condoms in the past. He doesn't like using then and neither do I. (I know stupid thing) but recently I switched my birth control from the pill to the IUD Marina. We have only had a quicky with it because he lives out state for school but will be home in two months. But my question is, my fiance wants to finish inside me. He's never done that before and would like too and personally I sort of want to feel how it is. What are my risks of getting pregnant for letting him finish inside me with the IUD?