First, most likely the Valtrex has nothing to do with your husband's abnormal liver function tests. Even though listed as a theoretical side effect, in fact in the early studies of acyclovir and valacyclovir (valacyclovir/Valtrex is really a version of acyclovir), the frequency of mild liver dysfunction was equally common in people on drug and on placebo. Further, even healthy people have occasional minor fluctuations in liver tests. That said, his ALT is fairly high, and I would wonder about other things that could explain it, such as a new case of hepatitis, or pehaps alcohol damage if he is a drinker, or any number of other causes. If his AST and ALT did not returned to normal after stopping Valtrex, he probably can safely resume it--but he should follow his own health care provider's advice on this. As to other medications, if his doc is not comfortable resuming valacyclovir, with his doc's approval he could try famciclovir (Famvir) or acyclovir. There is another drug, foscarnet, that conceivably could be tried--but that is a much more toxic compound; most likely his doc would agree it would be safer to resume one of the standard drugs.
In fact, your case is typical: the people who transmit genital herpes to others most often have no symptoms; or if they have symptoms, they don't recognize them for what they are. It is pretty common for herpes to first show up in a monogamous person after many months or years of repeated sex with an infected person. Even people with no symptoms whatsoever intermittently have active infections (called 'asymptomatic viral shedding'), during which times they can transmit infection to their sex partners.
Having said that, it is also possible your husband acquired his infection from some other partner. As an STD specialist, of course I see patients all the time in that situation, so you will understand why I bring it up. But only you can judge whether or not he is likely to have had other sex partners about the time he started having herpes outbreaks. Also, you don't say how your herpes was diagnosed 20 years ago and how certain your diagnosis is. If there is any doubt, you should have a blood test for HSV-2. It might be important--not to play detective about whether you infected your husband or not, but because it will tell whether you are immune (already infected) or might be susceptible to catching your husband's infection.
There are excellent online sources for extensive information about genital herpes. Try my former health department (www.metrokc.gov/health/apu/std), CDC (www.cdc.gov/std), and the American Social Health Association (www.ashastd.org).
I hope this helps. Best wishes-- HHH, MD