Brothers best friend..?

If your brothers best friend keeps trying to do sexual things and it makes you uncomfortable would you tell your brother or just leave it alone?

We're all adults here, I find him unattractive and like a half brother to me. But he won't stop asking to do sexual things to me. None of my brothers friends ever 'hit' on me until I turned 18, and almost 6 years later it's getting worse 🥴