Sounds like your are approaching this is a mature, logically thoughtful way and I congratulate you for this. If you will forgive me, before I answer your question I will may an observation and , I hope, a potentially helpful comment. You mention that your partner is having 3-4 outbreaks a year while on chronic suppressive therapy. In some instances people need more than a minimal amount of valacyclovir to achieve adequate suppression. It may be useful for her to talk with her health care provider and to modify her dose, going to twice daily suppression if she's only taking it once a day or 1.0 gram doses if she is only taking half that. The suppressive effect is, in part, dose dependent.
As for your questions. If you are found to have antibody your are largely but not entirely protected. Occasionally people who already have antibody go on to become infected in another site. This is sufficiently rare to be noteworthy but it does happen. That said, you are largely protected if you already are infected.
Regarding turn around time for the test, there are two factors which determine when you get your results--the time it takes to do the test and the time involved in shipping, getting around to doing the test (in some labs they are done every day but are batched), and how long it takes to get the results back to the person that ordered it. These latter factors contribute in the variability in how long it takes to get results back, not how long it takes to actually do the test.
I hope this is helpful. EWH