First off, let's just get this out of the way: Gone Home was the first video game to center a lesbian narrative.
Are you sure? Because I think that a number of visual novels have been based on lesbian romances since the 90's. And no, I don't think that they are all porn.
Admittedly, it is arguable whether some visual novels are games, but the same can be said for the "Walking Sim" style.
Love and tolerate.