Welcome to the STD forum. I'll try to help.
Before I get to your specific questions: When chlamydia first appears in an apparently monogamous relationship, and when that relationship has been going on for several months or more, by far the most common explanation is that the relationship in fact has not been truly monogamous -- i.e., that one partner or the other has had sex with someone else. That's not absolute, and no laboratory test is perfect. Of course, you are in a position to judge his fidelity and truthfulness; I cannot.
1,2) The tests used most commonly for urine chlamydia testing pick up about 90% of infections; and they are false positive less than 1% of the time. Therefore, it is unlikely that testing missed an infection you had last March; and unlikely that it gave a false result recently. It is most likely that you truly did not have chlamydia last March and do have it now.
3) If you had only had sex a few times when you were tested in March, indeed it is possible he was infected but you had not yet caught the infection. If you are confident your partner is telling the truth and has not had sex with anyone else in the past few months, then this is the most likely explanation.
4) Griseofulvin (Gris Peg) is an antifungal antibiotic, usually used to treat infection of a toenail or fingernail. It has no effect on chalmydia.
5) Usually when one partner is infected, the other also has a positive test. But as I said above, the test misses about 10% of infections, so it is possible for one partner to be negative and the other positive. (You don't actually say he has been tested. Has he? When?)
You and your partner both need to be treated for chlamydia, regardless of his negative test result.
I hope this helps. Best wishes-- HHH, MD
He actually got tested today i believe
Good. Just to be clear, he needs to be treated even if the results is negative.