Wow thats scary. I also have only heard of Acyclovir being used for treating herpes. Your boyfriend is probably imbarassed and scared that you'll leave him if you found out. Herpes is one of the most common std's out there, I think it's like 80% of the population have it. I would ask him and assure him that you understand and want the truth. I will attach some more information on herpes and Acyclovir below. Good luck.

Acyclovir   and   Herpes

 

Acyclovir is specific for the Herpes family of viruses but does not prevent transmission even if the user does not show any symptoms or skin lesions.  From a practical standpoint the risk will be less than if he is showing acitve lesions. if your boyfriend has herpes he should be taking this drug regualrly to suppress blisters and reduce viral "shedding" and you should use a condom in addition. This does not mean he has other diseases which must be tested for individually. You should both get a complete STD screen and go from there for your decisions.

Acyclovir is also used for cold sores, which are called Herpes 1.  Herpes 2 is the STD.