In need of insight

Okay so I am in a serious relationship for over a year and we have 3 kids all together 2 of which are mine and 1 of which is his and we madly in love! Well straight to the point lately for some reason i have not been so interested in sex but I do it just to keep him happy and I don't understand why I'm like this. It's not him or our sex life because that is amazing but the real question is, is there some way to make my sex drive stronger or to not make him feel it's his fault or that I'm still interested in him sexually?