My friends have asked me to elaborate on my Speedwagon x Straizo ship and make art of it (I WILL GIVE ME TIME)
But like functionally let me explain like how I view it.
I think they start falling for each other during Phantom Blood, get together after the end of Phantom Blood. Speedwagon has already given up and Johnathan, Straizo is kinda settling down with raising Lisa Lisa. Speedwagon is known to be gay and you cannot convince me Straizo is straight. They're both hanging around Erina, in close contact.
So I think they would have been getting close during Phantom Blood, even closer soon after. I think they would have become life partners (wearing matching rings but clearly not married because they couldn't).
Speedwagon is obsessed with the idea of growing old together while Straizo with his gerascophobia (fear of growing old) hates when Speedwagon talks about it.
Erina knows 100%, she saw them kiss once and they freaked out and she genuinely doesn't care as long as they're happy.
Joseph has 0 IDEA, they don't trust him not to start telling people they're gay.
Lisa Lisa knows, these are her gay dads.
HOWEVER I think by the time Battle Tendency starts the two have separated, not planned out when but likely around the time Lisa Lisa has to flee.
Idk I just think this makes the final interaction between to two so much more interesting and partly explains Speedwagon's grandfathery relationship with Joseph.
(Also we don't talk enough about how Joseph killed his mom's adoptive father his GRANDFATHER without knowing).