My fiance is the only I feel needs to know about my diapers, as they're a sexually charged object for me, and we try to fulfil each others kinkier desires when we can.
He's pretty kinky himself - he likes ladies panties and wears them most days, sometimes we pick out panties together or I find some for him to wear, so it helps that he's far from a prude. He's been nothing but accepting and supportive, but it's still always a little hard for me to bring myself to bring up the subject with him. I've come a long way, it's a lot less embarrassing now, but it's still pretty silly that it's even a little hard for me to talk about it when I know he doesn't have a problem with it... actually, he's growing to like it.
I've always been pretty shy and introverted so opening up to people and feeling vulnerable isn't something that comes naturally to me. It took so long to work up the courage to tell him in the first place, but it encouraged him to confess his interest in panties, and it brought us much closer together, so as hard as it was it was probably one of the most rewarding moments of our relationship. There isn't much better than confessing your strangest quirks and kinks to someone and knowing they still love and accept you, and to have them open up in turn.