Before Cas, Dean had been completely sure that he was straight.
Even after he'd realised that these feelings were definitely not platonic, he'd never questioned that belief. The fact that he was gay only fully hit Dean the first time he and Cas kissed.
It was different from any other kiss. For one thing, Dean had never felt such an explosion of emotion from something so chaste.
For another, Cas' lips were rough and slightly chapped and distinctly unfeminine.
Even stranger, Dean suddenly realised that he preferred this to the softness of a woman - it was so much more real.
Yep, he was definitely gay.