For what it's worth, many guys have urinary problems like this, without cheating!
That said, i is good that he asked you to get checked, too! That shows that he cares about you.
Do it! Find out if you have any problems! If you do, likely the doctor will tell you what the bacteria or whatever it is, is. If it ends up being an STD of some kind, that's a good indication that one of you MAY be cheating. BUT, some STDs don't show up for years. This may be something from someone that either of you had sex with, years ago! It does NOT necessarily mean that either of you IS cheating, now.
Get it checked and likely it will be nothing. At least you will KNOW!!
Best of luck!