The chickenpox virus is just that, a virus. There really is no medication they could have given your boyfriend in high school to help him get over the chickenpox. To know if the virus has affected his sterility, he can go to a fertility specialist and have a motility test done. This test takes a sample of his sperm, does a sperm count and also tells how healthy that sperm is. This is a pretty simple test and you can know quickly whether or not his fertility was affected.