Friendly reminder that Jensen was just the actor, not a writer or the showrunner. The actual writers of the show have confirmed and shown the exact opposite: yes, Dean did reciprocate.
There are multiple deliberate parallels between Dean and Cas and other couples on the show, which clearly confirm that their relationship was written romantically.
In the final season, the writers repeatedly used Sam and Eileen’s romantic relationship as a mirror for Dean and Cas’s. One example: when Eileen tells Sam she doesn’t know what’s real anymore because of Chuck, Sam kisses her and says “I know that was real.” This directly mirrors the scene earlier in the season where Dean tells Cas that nothing in their lives is real because of Chuck, and Cas replies, “You asked what about all of this is real? We are.”
Another clear parallel: Sam loses Eileen and Dean loses Cas literally in the same episode, 15x18. In fact, the entire episode where Castiel confesses was built around characters losing their love interests, starting with Charlie losing Stevie, specifically to set up and mirror Dean losing Cas at the end. The writers genuinely could not have made it any clearer.
On top of that, they introduced Adam and Serafina — a human and an angel who were deeply in love — literally one episode before Castiel’s confession. That was obviously not accidental. It was clear foreshadowing and an extremely direct parallel to Dean and Castiel. Everyone knows the biblical Adam and Eve story, but Supernatural deliberately changed the narrative specifically to mirror Dean and Cas — a human and an angel, just like Adam and Serafina.
They did the exact same thing with Cain. They didn’t even cast an actor to play Abel. Instead, they created an entirely new character, Colette, Cain’s great love, specifically so she could mirror Castiel in Dean’s life. Cain literally tells Dean, “You’re living my life in reverse,” and says that Dean will kill Cas first and then Sam. Since Cain killed his brother first and then his love interest, Dean living the story in reverse means Cas is his Colette (the love interest) and Sam is his Abel (the brother). That was extremely explicit. That is not subtext — that is text.
And finally, in episode 15x19, right after Cas’s confession and death, Lucifer impersonates Cas in order to manipulate Dean into letting him in. That is the ultimate confirmation that Dean reciprocated. The show had already established Lucifer’s consistent method: he always impersonates the person’s dead love interest in order to manipulate them into letting him in. He did it with Nick by impersonating his dead wife Sarah, with Sam by impersonating Jessica, his dead girlfriend, and with Vince Vicente by impersonating Jen, his dead lover. And he did it with Dean by impersonating Cas.
Therefore, Castiel is canonically Dean’s love interest. Destiel is canon. You cannot argue against these canon facts.