Can you get HIV from sitting on wet seat (worst case example if it was HIV semen about 30 seconds exposed in air)? Liquid went inside butt w/clothes

Forgive my surprise. You're almost a grown man and i'm wondering why you'd have a fear like this. You say you sat down where you have reason to believe that an hiv-positive male had just ejaculated, and that the fluid soaked through the back of your trousers and up there? Something else must be troubling you. Your personal physician is your best friend. Be brave, make the phone call now, and had an honest talk.