But at the same time, what exactly is 'being gay' period, not just 'in name only'? The characters treat the fact that they're attracted to people of the same sex as just one piece of who they are and don't draw attention to it because they live in a world where it is unremarkable. What, are they supposed to shout over every subspace channel something like 'I'M A GAY MAN AND I HAVE A BIG GAY BOYFRIEND'? Or walk around in drag? What would they have to do to not be considered 'gay in name only'?
Have a same-sex relationship. Simple as that. Don't have it be something that's asserted or made speeches about, just present it as part of the character's life, in the same matter-of-fact way you'd present a heterosexual character's attractions or romantic involvements.
In other words, do exactly what Trek Lit has been doing with gay/lesbian/bi characters for years already.