He wants to be exclusive but you're not sure he's serious

Asking for exclusivity is a words move. What matters is whether his behaviour over the past few weeks already looks exclusive. Check how often he initiates contact, whether he makes plans that last longer than a single evening, whether he introduces you to anyone in his life, and whether his app activity has dropped off or stayed the same. If he's asking but still keeps everything loose, that's a mismatch worth taking seriously.

Also notice what the message itself leaves out. A vague "let's be exclusive" with no mention of what that means day to day can mean he's thinking about the label more than the commitment. Someone who's serious usually has at least a rough picture of what it looks like. You're allowed to ask him what he has in mind before you agree.

Your reply should make the bar visible. You don't need to list demands. One clear sentence about what you need in order to say yes is enough, such as wanting him to delete the apps, or wanting to see more of each other's lives before you commit to exclusivity. That tells him what the decision depends on and gives you something concrete to watch for.

Keep the tone warm and the content specific. If you bury the condition in apologies or jokes, he may miss it entirely, and you'll be left wondering later whether he understood what you meant.

Send the reply at a reasonable time, not late at night when it reads as heavier than you meant it. If he doesn't respond for a day or two, don't treat it as a verdict yet, since people often need time to think about a question like this. If a week passes with no answer and no movement in how he's acting, that tells you something real. You can send one short follow-up that restates the question without guilt, and then let his response decide the next step. If he still goes quiet or dodges, you have your answer and it's fine to stop expecting this to become exclusive.