For those of you who are Supernatural fans....
Just my opinion here but I think the reason Dean didn’t say “I love you” to Cas is because he never could say those words. He didn’t say them to his father or Bobby or even Sam. Those were words that he was always afraid of saying, he always had a problem with them since his mom died as I’m sure those were some of the last words she said to him when he was a kid. The words “I love you” meant the person was leaving forever, they meant death for Dean. Permanent death, no coming back. And the fact Cas said those cursed words and was about to be taken to the empty only made that more real. Dean is a man that shows his love. The way he begged Cas, the look in his eyes, the tears. He loved Cas, he just couldn’t say it out loud. At least that’s what I think Jensen Ackles was trying to portray in the character. We all know it was a possible script for him to say the words back, that proof being in the Spanish version. But Jensen was sticking to his character, what he knew Dean would really say and while everyone is having an all out war over proof of Destiel canon and how the show ended, I applaud Jensen for making that decision for his character.