Tested hiv- 1 yr after unprotected anal exposure. is this conclusive? saw other similar posts & doctor have answered like "most likely you don't" why?

You don't: If you're negative one year after exposure, you can assume you are not infected. Failing to turn positive in a year is so rare that you would do yourself a disservice by continuing to trouble yourself. You're a young man, and many, probably most, young guys experiment with lots of things. That's fine and probably good. Be careful in the future, keep the memories, move on, and be safe.