i'm really worried

because i've been dating my best friend and my boyfriend for almost two years now. we started dating in high school and are now in college. he's in a completely different state for college and we get to see eachother rarely (one week every two months?): as you can tell, it seems to be a genuine relationship cuz our love lasts no matter the distance between us. but I'm really scared about telling him about how i have pcos cuz i don't know how he'll react to the idea of maybe not being able to have kids and i don't want to lose him. anyways, he knows that i have something, but accepts the fact 'i'm not ready to tell him yet'. I don't know, he seems to talk about 'when we have kids' goofing off but still, i don't know, i'm just afraid of how he'll react. when should i tell him? we're in a genuine relationship...i just don't want it to end cuz of something i can't help
