When I was in the same situation I kept the information to myself until I got my partner off. The only times it’s been an issue were when my partners felt self-conscious.

True you two had just met in person for the first time, but unless he had a cold sore there was no danger to either of you, and if that was his concern he should have used a dental dam.

Note to other readers: blood washes off of skin, hair, and fabric with cold water. It does not taste bad, it’s not gross, and it’s not a big deal.