It does indeed sound like prostatitis, and I'm sorry you both are dealing with it. The good news is that bouts of prostatitis do pass - it seems like it takes forever, but they pass. That nagging "have to pee" sensation is a real nuisance and annoyance but little by little it will go away until one day he just realizes it's not there anymore. That's been my experience anyway - I've had three or four bouts since high school but they all eventually went away. Antibiotics never seemed to help at all. Having the urologist do a "prostate massage" (which is basically just pushing on the prostate with his finger to purge fluid buildup) would seem to help for a couple days but that was about it.
The good news - ejaculation is thought to help clean the prostate out of bacteria and fluid. So, unless the pain after ejaculation is too severe, sex can actually help.
You're a good girlfriend to be trying to find help. Sorry I don't have better answers, but prostatitis is a nagging thing that basically just needs to run its course. He will get better, just give it some time.
Good luck,
Eisenhower