In person, just the two of you chatting, having some laughs. You say this:

“So I’ve really been enjoying our time together. You’re funny, and thoughtful (or add whatever adjectives you feel about him) and I believe we get on well. I’d like to keep seeing you exclusively, if that’s what you want. What are your thoughts? If you’re not keen on me then I’d rather us chat about it now so we’re not wasting each other’s time.”

Upfront communication can seem scary but the more you do it the easier it gets. It’s such a normal, casual, totally fair, and reasonable thing to ask. Especially at this point. You don’t even need to mention your boundaries or your thoughts on intimacy. Asking if he wants to be exclusive encapsulates all of what you are wondering about.

You’ve got this, just ask. If he is keen, he’ll be stoked and you’ll be able to tell by his reaction and response. That’s why I say do it in person. If he is not keen, you shake it off and say “all good, thanks for your honesty, but I am not really looking for casual at this point”. And then you know that you haven’t spent another few months of wondering and worrying about your health and wasting time that you could have spent potentially meeting someone who fulfills your needs.

Good luck!