I'm sorry to hear you limit skin exposure, unless you are just talking about using condoms, which is a good thing. I use medication and my partners and I pretty much let loose in bed, including body rubbing below the waist, unprotected oral on me, and anal and vaginal sex (with condoms). With some of my partners, the condoms give about 75% coverage of their penises. . With others, it's 100% or close to it. They didn't seem too concerned about "skin exposure" and as far as I know, I've never infected anybody.
I just wanted to make sure you weren't doing any bizarre body gymnastics to try to avoid "skin contact." With the medication, it's really not necessary. Hell, without the medication, it's not really necessary. Your risk of contracting it if he doesn't use medication is only like 8% a year.
As one of my (negative) partners said to me once, "just lie back and let me f**k you and eat you the way I want to" and stop worrying about it.
The antiviral medication really does work.
He's not going to become resistant to Valtrex. The drug doesn't work that way. If he takes it as prescribed (??500 mg q.d.), he will significantly reduce his shedding, which is how he can prevent transmitting it to you. If you guys are also using condoms, you are essentially coming close to 0 risk of transmission, or pretty darn close.
So basically, if he takes the medication, it works. If he stops taking it or skips doses, shedding will start increasing again. There is no resistance to it, no dependence on it.
I also only use medication to protect negative partners. We also use condoms religiously. I've never transmitted it to a partner that I am aware of. A handful of those partners were tested later after we stopped seeing one another and confirmed that they were still negative. The medication works. Between that and condoms, you are not likely to contract herpes from him.
Finger-to-genital contact on himself and then back to you is considered an indirect mode of passing the virus and therefore not efficient enough to cause infection. It's not enough to worry about. It's especially not worth worrying about if he is on medication, because the medication is what decreases shedding.
You don't have to worry about the "base of his penis" if he is on medication. The medication is doing the heavy lifting of prevention. Screwing the guy while he's wearing boxer shorts, if that's what you're talking about, is not only demeaning, it won't provide any further protection to you.
One more quick follow-up:
If he were to touch his genitals and was asymptomatically shedding at the time, then touched me in my genital region, is there a risk of transmission?