The one thing I can't do with my partner

My fiancé and I have a phenomenal sex life. I couldn't be happier. But I have a really weird hangup that I'd like advice in getting past. Because he really wants to do this one thing with me, and I want to make him happy, but....

It feels really weird to write this out because it seems so minor of a thing. But he wants to take a shower with me. And I'm intrigued by the idea, but I can't bring myself to do it because of some borderline abuse that I got when I was a teenager.

I got body-shamed a lot back then because of religious issues. I landed above average in the chest area, and a lot of the dads in my church were noticing. And their wives blamed me for it - it didn't matter how modestly I dressed. The rumor was that I was stuffing my bra in order to tease the men.

Not even close. What I've got is legitimate. But the rumors got so bad that my foster mom even walked in on me in the shower to confirm. I was humiliated.

I'm away from that foster family now and am looking for a way to move past this one incident... so I can make my fiancé happy. Ideas?