That seems very workable. There needs to be a plausible reason why they don't officially "go together".
That reason could very well be they realise that they would not work as life-time co-habiting partners. They would, however, care for each other very much (as friends do) trust each other, like each other (love each other as dear friends) but still not be "in love with" one another.
They would enjoy sex with one another when they have it - the earlier suggestion from the OP that it'd "feel wrong" when sober but OK when intoxicated does not ring true and seems to bring about Unfortunate Implications
regarding them taking advantage of one another while "under the influence".
While sober, sex would not "feel wrong", but it'd be "just sex" with no connotation of "being a couple" attached to it.
"I'm horny, you're horny, we like and trust each other, let's do something about it." sort of stuff rather than "I'm drunk so I'll do something that I would feel wrong about when sober".
From my own experience of having fuck buddies, it's not something we were ashamed of or felt wrong about. It was nice fun sex with a trusted person (rather than some random stranger met at a pub whom you never see again).
On the plus side, when you're together you can hang out and chat or do other things you enjoy doing together (watching vids, arguing about religion, whatever) or you can fuck, no obligation to do anything in particular.