I have talked about Geoffrey's identity as a bisexual man and how he feels about it before, but it was years ago, so to recap: internalized homophobia up to here (I'm holding my hand up very high because he's very tall)
But it's also... not exactly internalized homophobia. Like with literally everything else about this man's psyche it's complicated. He had inklings when he was a kid that he liked boys, but it was something he more or less just ignored until he got a little older and feelings started turning into desire. And in the hypermasculine Priwen environment it became very clear to him that there was a sexual component to his interest, that it went beyond just really liking some of his friends. To make it clear he never engaged in any kind of relations or relationships with other Guards, there was nothing untoward going on -- everyone either viewed him as the kid they found on the side of the road or the scary untouchable leader, and he was careful to maintain boundaries from his side as he came into leadership especially . But he was around men all the time, and saw and experienced things that made the proverbial lightbulb go off. So yes, he's always been aware that he's attracted to women and men.
The problem comes with internalizing that attraction, let alone acting on it. On the one hand, Priwen wasn't particularly concerned with sex or sexuality. People that fell in with the Guard tended to be those who had lost friends or family, people who didn't really have a lot of personal attachments and weren't very pressed about relationships by extension. They had Chaplains in their ranks, there's a component of faith and religious weaponry in vampire hunting, but it's not as though the Guard was a religious order. But Geoffrey got it into his head early that he couldn't have anything outside of the hunt. So in that regard gender didn't matter, any relationship, any level of want was a distraction and a no-go. Bottle those feelings all the way up, if it's not hunting it doesn't matter. But also it was the early 20th century, which wasn't exactly an open and accepting time. Yes he grew up and lived in a homophobic society, and that did impact him. What other people were doing wasn't his business -- again, if it's not vampires it's not his problem -- but he did internalize ideas about being less of a man for wanting to be with other men. But that roadblock is less significant than his mindset of not being allowed anything outside of Priwen, so it's not exactly standard internalized homophobia. Just a lot of repression in a lot of ways.
Didn't always stop him from acting on his desires, though. Pre-game he's been with a few men (and women) sexually. All fleeting encounters with people he expects never to see again, in very 'it's not gay if you're on top / not the one sucking dick' ways. Beyond that I'll keep things vague because I don't like canonizing ships for rp purposes, but whether it's acted on or not I do think he had feelings for both Edgar and Jonathan (and for tragic purposes I'm inclined to say he didn't act on his feelings in either case until much later, if at all). Regardless, chastity has not been one of his virtues.
It takes decades and general social change for him to start taking his attraction seriously. It's wrapped up in a lot of what he starts to untangle about his sense of self after leaving Priwen. Little by little he comes around to the idea that he can Want Things and even Have Things without the world imploding. There is (un)life beyond Priwen. And he meets more people, and the world does change. Over time he realizes that any of his thoughts about being lesser for who he loves can't be true, because he doesn't think that way about other queer men. He's just lived a life with too many self imposed rules. The exact timeline of things and the exact way his feelings start to thaw are another thing I don't want to concretely canonize, because it's more fun to explore, but as a general timeline -- by the 50s/60s he accepts the fact that his attraction to men is legitimate and not something he needs to repress or ignore, and then around the 90s he starts to actively identify with the bisexual label.