Okay, well unless you have a weak bladder and have experienced accidentally wetting yourself at your age, then it’s highly unlikely that you’re actually going to pee.
It’s actually a very common sensation when approaching orgasm and often it’s a symptom of the G-Spot orgasm which can also lead to “squirting”. If that happens, a clear liquid (NOT PEE!) would come out.
The only thing you can do is accept the feeling and let it happen! Just give yourself over! You’re not going to pee on him. To give yourself more reassurance, try urinating before doing anything with him, that way you KNOW you have an empty bladder when the feeling comes around again.
Let yourself cum! It’s going to be okay.