Thank you for replying to me. I went to my doctor today and should have my results in next werk. I asked my doctor as well as posting it on here and they both told me it wasn't possible either. Thank you for answering my question though. :)
I hate to confirm you worst fears, but I have to suspect you're not getting the straight story here -- that your partner is setting up excuses for his infection. With a diagnosis of urethritis, he has an STD -- chlamydia, gonorrhea, or nongonococcal urethritis (NGU). There is absolutely no way he acquired it nonsexually, either from his mom's possible chlamydial infection or anywhere else.
In theory, some cases of NGU might arise because of adjustment to normal bacteria in a partner's vagina (yours) -- in other words, not because you have a recognized STD and not because you have had other partners. However, the more likely scenario is that he has had other sex partners.
If not yet done, your partner needs to be tested for chlamydia and gonorrhea. You also should be tested -- see your doctor or clinic (wherever you go for contraception would be fine) ASAP for examination, testing, and treatment. Do not take any antibiotics before you are examined and tested. Do it soon: you probably are at risk for serious complications, like pelvic inflammatory disease (PID).
Please come back with follow-up comments about the results of your and your partner's STD tests, and what treatments you were prescribed. Good luck!