A feeling of needing to urinate frequently could have many different underlying causes, ranging from having had a lot to drink, to a urinary tract infection, to prostate inflammation/infection, to a sexually transmitted disease.
It's probably a good idea for your boyfriend to see his doctor to determine the root cause of his symptoms so they can be treated (if necessary).
He could also have an enlarged prostate or a bladder infection. Ask the health care provider to give him a urinalysis, which can be given in the office, or get a referral to a Urologist and get checked out.
I am sure there are a few reasons. One that comes to my mind though is anxiety. If he is preoccupied with a stressful event (previous or present) this could be the cause.
Urinary tract infection is another.