
Yes. Even if they never interact with a guest, it’s common courtesy to inform people who’s going to be in the place they live. Plus, there may be a level of comfort between roommates that doesn’t extend to guests, so a heads up so they can just be aware and adapt their behavior accordingly is basic kindness and respect
It’s your space too, and you deserve to be comfortable there. I would just sit your roommate down and tell him that he needs to let you know before any guests show up, no matter who it is or what they’re doing. Full stop. If you’re living in a dorm, this is the kind of issue you can escalate to your RA if it doesn’t stop, otherwise if you provide anything for the dorm then you can use that as a boundary/ultimatum. As in, if he can’t respect you, he can’t use your xyz anymore.