How to ask if he wants to be official without seeming desperate

Ambiguity isn't accidental. It's easier for him than commitment. He gets closeness without risk, your time and attention without any explicit promise back. That doesn't mean he's a bad person. It means he hasn't had to think about what he wants yet.

When you bring it up, you're creating a moment where he has to choose. That's the whole point. Until now, staying quiet has been his option. You're removing that option. Watch how he responds when comfort stops working for you. People show you who they are when they can't coast anymore.

Don't ask him to guess how you feel. Don't make it a test. Tell him clearly what you've noticed (you've been together for X time, things feel good) and what you need to know (whether he wants this to be exclusive, whether he's seeing other people, what his actual intention is).

Then stop. Let the question sit. A good reply here acknowledges what you said instead of redirecting to something easier. He either gives you a straight answer or he shows you that he won't. Both are information you need.

Only ask this question if you actually know what you'll do if he says he doesn't want something serious. If you'll keep dating him anyway because you're afraid to be alone, wait until that's not true anymore.

Send it at a normal time when you can have a real conversation, not at midnight. Give him a couple of days to respond. If he ghosts you, takes a week to reply, or responds with something vague, that's him answering without words. At that point you know. Don't ask twice. Don't soften the question the second time. Just decide what you do next.