The important thing about this is that Dean has never at all denied the insinuation of a relationship with Castiel. If he is as much of a heterosexual legend as canon claims him to be, maybe he would have tried to defend his sexuality more adamantly. But I don’t think Dean is straight, and I don’t think he’s gay either. He is certainly sexual with women, but he doesn’t seem to be able to interact with them on any deeper level. Even his relationship with Lisa was founded on not his attraction to her, but the idea of her, of being normal. While, yes, he has sex with women, all his emotional relationships are with men, so at the very least he is homosocial. The interesting thing with Castiel is that there is no familial obligation that keeps them together- not like it does with Sam or Bobby. The level of trust and affection he has for Castiel is homo-romantic I think, and the fact is that if Castiel was played by a woman, they would have had sex ages ago. Dean is loud, brash- but he makes no attempt to deny that Castiel has feelings for him, he doesn’t even laugh it off like he does the other gay jokes. He acknowledges the feelings between him and Castiel by not talking about them, by refusing to comment because they’re not feelings that can be easily resolved, and it’s just fucking complicated.