My brother is ABDL

Thanks for reading, Idk if this is the right group but I'm at a loss right now. My mom told me yesterday because she's at a loss too on how to handle this. Little background, my brother will be 20 in September. I am 11 years older than him and helped raise him as a baby/child while my mom worked nights. She has known for a few months that something was going on because he still lives at home and shes found a few things he left under the bathroom sink (some type of chastity belt?) He came to her yesterday and said he has an incontinence problem and went to the doctor who told him to just wear diapers. My mom knew that was a lie and asked him to go see her doctor, hes 19 years old never had a problem before, no reason the doctor wouldnt run tests and try to treat him. So an hour goes by and he tells her in text that he lied, he is in the ABDL community and likes to wear diapers. My brother really struggles socially especially with strangers and doesnt have friends, only friends online. This is some fetish he has developed, which everyone is free to do what they want privately but this, idk. How do I accept this and how can I help him? Is it something that I did or didnt do when we were kids? I was 14 taking care of 2 babies, is it my fault? I worry so much that he won't be accepted by society, people won't understand this. People in my family will not understand this. I've been crying on and off since she told me, which she agreed not to tell anyone else but where do we go from here? He wore one under his clothes to our sisters graduation (now that I know it is noticible in pictures) and mom said he came home from work waddling yesterday, so he must have worn one to work and possibly used it. He told her he has no attraction to children, but he likes wearing diapers. Advice please?