OUGH I love slow burn Billford. Bitter exes constantly fucking is good too but there's something about neither of them confessing any feelings until the last possible moment that is *chefs kiss*.
Like, pre-portal, Ford assumes any strong feelings are just reverence for his muse, and Bill thinks his strong feelings are just sadism, the fun of using Ford, nothing more. Fucking during karaoke doesn't contradict this, I think Ford probably couldn't remember, or maybe his memory was erased. Bill was still in denial, fucking Ford was 'all part of his master plan' somehow (or maybe he just forgot too). Whatever happened that night, the next day, I think they both sensed something had changed, although they couldn't put their finger on what. All they know is that whenever they're apart now, they can only think about each other.
Bill doesn't figure out that he loves Ford until the break up, I think that's clear in Tbob. But I really like the idea that Ford doesn't figure it out till weirdmageddon, and that he refuses to believe that Bill loves him.
To me, it feels very in character for Ford to brush off Bill's very obvious flirting as just a humiliation tactic. Ford has very little self-worth. I don't think he believes anyone would love him for him. People only love what he can do for them. He's also autistic coded, aroace coded. I think he finds it hard to actually recognise romantic advances, even if they're laid on real thick (we see this with fiddleford too). And lastly, there's a lot of shame in being loved by a monster like Bill. It's probably easier to deny it, bury it deep down instead of dealing with the survivor's guilty. Pride and shame are big thematic throughlines in Ford's story.
I also think it's really in character for Bill too. Bill thinks love is weakness. I think he's embarrassed and afraid of how down bad he is. And so, all through the portal years, he's trying to tell ford that he loves him, without telling him. And it kinda comes off as bullying. You can't really blame ford for not picking up on it. However it's funny to think that all the henchmaniacs have.
Anyways, I like to imagine that it doesn't click for Ford until they're alone in the penthouse, and Bill has him pinned. He's finally showing Ford how genuinely frustrated he is with both Ford and himself. He really hates that he loves Ford. He's still really hurt that Ford abandoned him. He really does just want to rule the universe with him. And ford is somehow shocked by this revelation because he's a fucking idiot.
Then, and only then, does Ford finally realise that he loves Bill too. And it hurts so much because it doesn't matter. Everything's gone too far, love can't save them anymore.
I think about this all the time.