I am not a professional botanist, but I'll give this a stab. Maybe some one
else has a more detailed answer.
There are many different inherited mechanisms in plants to prevent
self-pollination. I don't know the precise ones in cherries.

Presumably this seed has DNA from both A & B.
The question is which self-incompatibility gene it inherited, if any.

When this seedling matures it will require a pollinator in order to make
cherries.
The word you want is pollenizer. The pollinator is the bee.
You don't know offhand which pollenizer the offspring will require. A
professional pomologist might. At any rate, as I told the fellow looking for
apple seedlings, it is not practical for the amateur to try growing fruit trees
from seed, as they take many years to produce fruit, and very rarely produce a
superior variety.

In species where varieties are self infertile, how is it that the varieties
can stay in any way distinct?
They are only propagated vegetatively, by cuttings, grafting, or meristemming.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)