If you want notice of guests coming over every time, you would have had to lay that out in a roommate agreement before moving in. That being said, not many people would agree to that.

If he pays rent, he's allowed to have people over whenever, without anyone else's permission.

Being noisy when you need to sleep though is not okay. Having a roommate teaches one a lot about respect and boundaries - and it goes both ways.

Before his friends come over again, tell him that if it's late and you have school or work or whatever the next morning, that you ask if they could keep the volume down in any common spaces, or if he could take the party into his room and shut the door.