My cat has had rhenotracheitis for a month. how long can it last?

UNFORTUNALY I BROUGHT I CAT WITH THIS ILLNESS AND IT GOT ALL OF THE OTHER UNVACCINATED CATS SICK. ONE PED AND THE REST GOT BETTER, BUT THERE'S STILL ONE BADLY CONGESTED. I FEED HIM, ADMINISTRATE FLUIDS INTROCUTANEOUSLY, GIVE HIM L-LYSINE, AMIXOCILLINE(50GRMS), YOGHURT, HILLS, SPECIAL DIET, TUNA FISH, PILLS TO STIMULATE HIS APETITE. I REGULATE THE ROOM TEMPERATURE AT NIGHT AND KEEP IT COOL AT DAYTIME.I GIVE HIM SALINE DROPS (FOR KIDS) FOR HIS NOSE. BUT HE'S STILL SICK AND ACTUALLY STABLE. SOMETIMES HE GETS BETTER BUT HE HAS SOME RELAPSES. HOW LONG CAN I EXPECT HE'LLCONTINUE LIKE THIS UNTIL MAYBE HIS IMMUNE SYSTEM BREAKS THROUGH?