I had always had trouble taking a load of cum in my mouth. I couldn't stand the thought of swallowing, and trying to hold a guy's juice in my mouth left me choking and gagging. Sometimes a trace of puke would rise, and then I would have to let go of the cum, "cum" what may. The results were usually not pretty, so I avoided giving head.
My first male suck-off partner was always in a hurry to finish. He was also my first male partner, period, and the head I had gotten from women previously was pretty limited, so I was deep in the dark about head. I later discovered that what he was giving me was not a blowjob, but a hand job with his mouth atop my cock.
Then my sister-in-law died. My no-good younger brother had abandoned his family years ago, but I was still the beloved uncle to his two children, their favorite uncle. That's not saying much, because their other uncle, my sister-in-law's brother, was an even worse rotter than my own brother. After her family picked over her belongings and took what they wanted, a Water-Pik remained, so I inherited a Water-Pik. Never mind what happened to the children. That's another story. The important part of the story here is the goddamed Water-Pik, of all things!
When I first started using it, I had the same sensations of choking that I had had with cum. I practiced and practiced for months consciously closing the rear of my throat until I could almost always do it as needed.