My boyfriend likes to wear diapers. How do I help him to become more comfortable with this part of himself?

How can i help him become more comfortable with it? He's really worried I'll become disgusted with him and leave even though I've tried to reassure him I'm perfectly ok with it. I know its not a sexual thing its an emotional comfort thing. he's autistic and deals with anxiety and possibly depression. I just want him to be comfortable with this part of himself.
My boyfriend likes to wear diapers. How do I help him to become more comfortable with this part of himself?
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