What can be done about my Autistic cousin who says he needs a colostomy to be free again?

I’m 17 and my cousin is 26. We aren’t all that close but we see each other like every other weekend when I visit my aunt. He has autism but is high functioning and smart in certain topics (he has a college education) but he is pretty much a hermit and only leaves his house to visit our grandmother a few blocks over. If he ventures out farther, especially by car, he gets a panic attack and has to go to the bathroom and my aunt has to turn right around and bring him home. He is petrified of diarrhea and even developed an eating disorder because of it.not eating disorder in the sense of body image but he’d eat only small amounts of certain foods in order to avoid diarrhea, which I think is a major sensory problem and phobia he has. He is completely healthy other than the problems I mentioned. But he spends so much of his day going back and forth to the bathroom and can’t hold it in and it isn’t diarrhea at all but he just always feels the urge to go and does. He eats fine now and normally has unnaturally hard stool he says, but once in a while he gets what I think is quite normal to most of us but he freaks out because it is “too soft” and he makes himself sick over this. He is so crippled by this that he even confided in me that he wishes he could have a colostomy bag so he doesn’t have to worry about being near toilets when he goes out and that it’d give him freedom and he’d finally be able to live and get out of the house. He researches it all the time and is convinced this is the answer. It seems a bit extreme to me, especially when that is major surgery. I don’t understand if this is a legitimate reason to consult a colon doctor about or if this is a severe phobia, mental disorder that needs to be addressed. What do you think? I’ve searched google but only find phobias of vomiting, not of the bowels. With all honesty it makes sense that an ostomy bag would solve his issues of fearing of going to the bathroom all the time and I’d love for us to hang out other than only in his bedroom, but it seems a bit extreme. He’s intelligent but like I said, he has autism and can’t live on his own and can’t deal with a lot of everyday tasks and obsesses over things. I’m concerned and just want the best for him. He has no friends. My aunt made an appointment with a psychiatrist but he won’t see him til late July. I think he just needs intense cognitive therapy, but does he have a legitimate reason for getting a colostomy bag, especially if he is certain it’d turn his life around?