If you didn't like it at the time or are suffering ill effects afterwards, it was abuse. "Normal" experimentation does exist, including between brothers, but it must always be consensual, mutual, and avoidable / end-able by vote of either involved.

Having just read your Survivor Story and some of your older posts I'd say its clear you were abused - because you yourself angrily and ruefully broke it down as such and detailed the damage, for so many years. "Maybe it wasn't so bad" is a form of self-minimization that probably all survivors of abuse and trauma go through.... trying to make it go away through intellectual reasoning. If you could reason your way past feelings, no one would be here.

My story

"Don't think it hasn't been a little slice of Heaven just because it hasn't!" --Bugs Bunny