What is it and how is it passed on?
Non-specific urethritis (NSU) is an inflammation of the urethra (the tube where urine comes out) that affects men only. It may also be called non-gonococcal urethritis.
It is usually caused by vaginal, oral or anal sex with a partner who already has a sexually transmitted infection (STI). It's called 'non-specific' as a variety of infections can cause it.
Other causes include:
other genital or urinary tract infections
damage to the delicate urethra through vigorous sex or masturbation
a urine or bladder infection, although this is rare in young men
You can't catch NSU from kissing, hugging, sharing baths, towels, cups, plates or cutlery, or from toilet seats or swimming pools
So he could have got it from just masturbating a lot. Although not standard cause for this it is a possibility... so technically if he has it it is an std but it doesnt mean he got it from you or any other girl for that matter.
Very much like when we girlies get thrush, not neceassary a sex thing.