I think what really sold it for me was my headcanon that Kaidan was straight, but then the right "human" came along who happened to be male, broShep's death possibly startling Kaidan into becoming more openminded about their relationship...
Well, he must've thought he was straight, I suppose
I'm not bi, so I don't really know how that works. I headcanon it like any other relationship... they were colleagues first, colleagues who grew to respect one another and eventually like each other as friends (and perhaps more). The fact that Shep was a commanding officer probably made things too weird. And maybe Kaidan, who's clearly bi (even if it wasn't scripted at the time
) had less-to-no experience with men, so felt awkward about pursuing things. Then you have the various showdowns between them in ME2 and ME3, and finally, just when the world's about to end, he's like, well, f*** it. I like you, damn it lol
That's part of the reason I like the thought of Cullen NOT working for the inquisitor. I don't want my inquisitor to be his superior ... it will just feel wrong.
Course I'm kind of like you and thinking we won't get the chance to find out with our quizzy fellas, but we'll see 