yep. I agree.. You where fine until the river or when he shoved all-in. At best you should of flat called with the 2nd nut depending on how pot committed you were. If my math is right, you could have flat called on the river and only lost... what about $2.00. A lot of players will not play king high flushes for this reason. I like playing them and have had a lot of luck with them. However, I don't fall in love with it even when playing a loose or donkey player. Remember, even a donkey gets a great hand every once and a while. If he is bluffing
you , so what, let him bluff you. Fold or flat call and live to play another round. I have folded a lot of them on the river myself, especially in cash games. But, better yet, I have read many a poker book that says when in that situation the correct thing to do is to just call. When you could have the 2nd best hand and last to act you never raise!!! So, to answer your question, your raise when you could have called was your mistake.