"Functional" is a stage - for the alcoholic, and in my case it was trying to accept that the alcohol was a bigger problem than I wanted to admit to myself.
I will say, he always looked functional on the outside, but as soon as he felt "safe" enough with me to let his walls down, I realized that XABF was a nervous wreck and "wired for sound" (as he put it) 100% of the time.
It reminded me of when I was learning to drive, the car I learned in had a "handle" above the glove compartment, and my mother was always gripping that as tight as she could, until her knuckles turned white as a ghost, as soon as I turned the key in the ignition, before I even took it out of park.
XABF went through life like that, clinging on for dear life, white knuckled, terrorized - without any logical reason, and only the alcohol to agree with his terror.
What a sad, lonely, draining way to live. This was his "functional."