It sounds like infected or inflamed hair follicles from shaving, and not herpes. SIllyMistake is correct - there's no risk from mutual masturbation.
You use the word "accosted", then describe this as if it was consensual. Was it? I just want to make sure you know you are allowed to say no.
"I know without direct examination and test it’s going to be hard to diagnose"
Pretty easy. Mutual masturbation exposes you to no risks so there is no risk to this event.