It sounds like your average outbreak interval varies between 1 and 2.5 months, so maybe 8-10 outbreaks per year (?). Most people have fewer recurrences, and in most people the frequency of recurrent outbreaks gradually declines over time. But outbreak frequency you describe isn't all that unusual; it doesn't mean an abnormal immune system or anything like that. Valacyclovir does not cure the infection, i.e. does not eradicate it from the body. That is why recurrent outbreaks reappear a few weeks after you stop the drug.
There is no evidence that valacyclovir or acyclovir has any build-up of toxicity or tolerance even after several years treatment. Many people have been followed for several years on treatment, without any observed problems; the "no available data" statement about one year refers only to the manufacturer's formal database as submitted to FDA. And there is no theoretical reason, based on the chemistry of the drug, to suspect undetected, rare long-term side effects. That's not to say it can't happen, but the risks appear to be very low.
However, do not be tempted to take the drug on and off for weeks at a time. It sounds like you might be doing this some of the time. Either take it continuously, or take it for just 2-3 days for each outbreak. Other patterns of use will increase the chance that your HSV-2 strain might become resistant to the drug, making treatment all the more difficult.
I hope this helps. Good luck-- HHH, MD