What is the ruling of Islamic law regarding my suffering from obsessive doubts about purity (wasaas al-tahara) when urinating, and the resulting prolongation of cleaning time and physical and psychological distress, and what is the solution to overcome these obsessive doubts?

The cure for obsessive whispers (waswas) is to ignore them, turn away from them, and pay no attention to them. So, if you doubt whether you were splashed with urine or not, the original principle is that nothing has touched you. Do not rule that anything has been afflicted by urine unless you are absolutely certain with definitive conviction. Do not wash any part of your body, or the places you walk or sit on, unless you are certain that impurity has transferred.