What is the permissible area for wiping to cleanse from urine, and does the tissue touching the side of the urethral opening during wiping necessitate washing with water?

You are one of those who suffer greatly from obsessive thoughts, and therefore you must ignore these obsessions and not give in to them. The area for which istijmar (cleaning with stones/tissue) is sufficient concerning urine is half the glans or less. If the urine extends to more than half the glans, then washing it is obligatory. The glans is the tip of the penis above the circumcision site. Placing the tissue on the tip of the penis and wiping in the manner mentioned is sufficient.