does acyclovir have any other use besides treating herpes?

 It only treats herpes that I know of.  You don't have to have signs of it to spread it.

http://www.webmd.com/genital-herpes/news/20081030/herpes-often-unknowingly-spread

It treats all forms of the herpes virus, including chicken pox, shingles, cold sores and genital herpes.  It does not cure the virus, in only inhibits its reproduction, thus shortening course of an outbreak and limits viral numbers and can decrease the chance of spreading the virus.  Best if taken at the start of an outbreak.  Short term use is typically harmless but long term requires a check of liver function as it can cause hepatitis.  

-Oral herpes (cold sores on the mouth)
-Genital Herpes
-Chicken pox
-Shingles

Thats it.  

Also, I have a bottle of Valtrex (which is the same thing) in my medicine cabinet from a misdiagnosis.  There ARE drs out there that just take one look and automaticly assume that it is herpes.  Some doctors diagnos without taking a blood test.  Which is so unprofessional.  
 
Before you confront him ask yourself:
-Is there any time that he doesn't allow you to see him naked?
-Is the date on the bottle recent? within the last year?
-Does he ever get cold sores? Or has he ever had one in his lifetime?

There are other uses for Acyclovir as the above poster listed but it's mainly used to treat herpes.
Acyclovir is  suppressive medication. If he takes it regularly then your chances of getting herpes would be reduced. Also if he does not want ot have sex once in a while then this could be a sign that he may have out breaks. You should not have sex while he has an out break. The rest of the time there would be less then a 10 percent chance of you getting herpes from him, this would be even further reduced if he is taking medication.
You don't always need an out break for herpes to be passed on there is just more of a chance of it being passed on while there is one.
Maybe you should have a private talk with your boy friend and tell him what you found then ask him if he has herpes. If he says that he does then it wouldn't hurt to go and get tested for herpes.

It is used to treat shingles too. Shingles is also very common.

It can also be used to treat oral herpes (prevent cold sores on the mouth) as well as treat genital herpes,

The herpes virus family is a group including mono, chicken pox, shingles and genital/oral herpes. Acyclovir can be used to treat a range of these.