Forcing feeling?

Me and bf got into a conco and he explained how he was unfaithful with his ex because it was long term he felt he git tired of sex with one person nd ended up cheating. I asked him how would he be faithful to me then and he says he forces himself i automatically got upset because i feel you should naturally only one to be with that one person if you have ti force yourself it seems like a problem. Idk am i overreacting or looking at this the wrong way