Ah, Guy, you know better than that. Fatherhood is no proof of heterosexuality.Even though he was the only one to reproduce?
For what it's worth I always liked David. I like that he was his own person and not just a Kirk clone. That he wasn't a traditional macho man idealistic traditional son that an alpha male like Kirk would've been expected to spawn.
The novelizations had him having a relationship with Saavik which was interesting, and funny enough for this topic the actor was gay. While he never came out publicly it's well known he was gay and his Square Pegs co star Sarah Jessica Parker casually outed him in an interview years ago, as I don't believe she was unaware he wasn't out in the media.