Hi,
My answers to your questions are indented for clarity:
"I need to know if a female can pass NGU to her male partner without her having had sex with an outside person."
Yes. (but so you know a female can't really give you NGU; NGU means inflamation of
the urethra, what she gave you is a bacteria/parasite that causes inflamation of the
urethra)
"I ask if a monogamous male partner in a relationship gets NGU, is this proof positive that his female partner has had sexual activity outside their relationship,"
(this is really the same question, stated differently) The answer is No.
"and does this sexual activity outside the relationship have to be full vaginal, oral or anal sex or could it be caught from less intimate activity (and if so what less intimate activity)"
You get NGU from insertive oral, vaginal, anal sex.
Or you can get urethritis if for example you dip your penis in beer, and grind it in or
masterbrate with beer on it, or such a substance that will cause irritation like that.
"If infection of the male or female from non sexual sources is possible, what might these non-sexual sources be?
NGU is not really a non-sexual. If its non-sexual its a UTI. If sexual they call it NGU, a
bacteria from oral, anal, or vaginal sex that is not gonorrhea.
Further to previous information given, condoms were being used for contraceptive purposes, but there was some unprotected genital contact prior to donning the condom.
Also, female partner reported that checks for STIs at her clinic were clear. There was some Thrush on occasion.
Yes, it was cured. We both attended clinics some distance apart (whilst working away) at the time.