Kissed my boyfriend who had a dry cold sore? Should he be virus-free at that point?

Never... ...A guarantee - but then again, some people are contagious without a visible lesion.
No. A patient that has herpes simplex is never virus free. After initial infection, the viruses are transported along sensory nerves to the sensory nerve cell bodies, where they become latent and reside lifelong. You may be immune to the virus due to previous exposure but do you want to take that chance. I would not. Acyclovir prescribed by a dentist or physician will help heal the lesion.
Never. Once you have herpes simplex in your body it never goes away. Even in the absence of overt lesions there may still be viral shedding. My bet is that if you were tested it would show that you have developed antibodies to this, showing that you were previously infected, but not everybody becomes symptomatic.