brother keeps master baiting in the room at night while I'm awake...

title wouldn't stop autocorrecting masturbating. idk why. anyways.

he does it every night and even when I'm clearly awake, like I have my phone on and out, I'm sitting up, or make a semi loud noise. he just keeps humping away at the bed. and... it's a normal thing for guys to masturbate everyday, or so I've researched, so I've tried to tolerate it, but I have to put my earbuds in and blast music at near max volume because even hearing it slightly makes me feel so disgusted and angry atp even. it's gotten so bad that any sounds like fabrics rustling against each other immediately bring up that image/thought and I hate it.

hes autistic which might be affecting this, but he does it and then js sleeps in the same bed (he humps the sheets....), wears the same clothes, etc... it gets really smelly sometimes and idk what to do or how to tell him without really hurting him since I know autistic people have rejection sensitivity dysphoria and maybe if I tell him wrong he'll shut down. and it's not like it's bad, he js needs a better way to do it. and a better time...

for context ig, I'm his older sister, we share a room (not enough rooms in the house for everyone to have their own), and has been going on for what feels like months if not years.

I need advice on how to communicate this to him without majorly hurting/embarrassing him (other autistic people commenting on this esp would really help) and then alternatives for when/how to do it.