I have yet another question

This time about the likelihood that our new cat could have feline leukemia but is not yet producing antibodies that would result in a positive test... and how long we should wait before introducing our cats if there is even a remote chance that new cat could be infected.
We have a 1.5 year old female cat. We adopted a male cat (approx 1 year old) last Wednesday. He was found outside (we don't know how long he was out there or where he came from). He obviously is not feral because he is fixed and is very people friendly. The people who were feeding him tried to see if he was lost- posted notices in the community and the internet, looked for a microchip, scoured the lost ads, etc.
On April 18, the people who were feeding him took him for a checkup and got him a distemper shot. He tested negative for feline HIV and leukemia. But he was outside for about a week and a half after that.
On May 6, we took him for his distemper booster and another check up. We wondered if we should get him tested for leukemia again. The vet told us that if he was recently exposed he probably hasn't started producing antibodies yet. She said we should test him again in 6 months. We told her we don't know if it was realistic for us to keep the cats separate for 6 months... so then the vet said we could get him tested again in 6 weeks...and in an ideal world, we would keep them separate until then, but he is probably low risk because he already tested negative.
We're really confused. The vet acknowledged that she gave us sort of a "non-answer." I assume she has to err on the side of caution and can't advocate introducing them if there is even a slight chance our male could be infected.
But I'm wondering if we are just being too neurotic? Can anyone give any advice? Would you keep your cats separate for 6 weeks?