Diane, your situation sounds much like mine, similar age, didn't do treatments until very recently, wasn't obvious i had a health problem in past relationships.
I too have found a man now who seems to be very supportive, but like you I am reluctant to let go and just 'trust' that he'll stick around.
He already has a son, so at least I don't feel that i'm preventing him from having kids, which is a biggie for me, i always feel i have nothing to offer a man.
Diane, if you feel so strongly that he is the one for you, i have two very very important pieces of advice:
1) throw yourself in their boots and all and do NOT question it, just enjoy it, you deserve to be happy as much as if not more than anybody else. Don't second guess it, god has sent you a gift, unwrap it (often!!) hehe
2) make him go on top! <img src="i/expressions/face-icon-small-happy.gif" border="0">