Think about your limits, about what you can put up with, and what is going too far. You certainly don't have to tell him, because it's futile anyway, but your actions will speak for you.
Does he come home and leave a mess everywhere? You won't clean up after him.
Does he ask you phone work when he has a hangover? Nope.
Want money from you for buying alcohol? No, again.
Is he spoiling your night's rest - different bed.
Get argumentative? Walk away.
You don't have to tell, just do.
Some good starter boundaries are that you won't enable him by transporting, paying, lying etc
Be careful of boundaries you're not committed to, or aren't practical. Think about how you'll follow up and what the consequences will be.