Translation:I will never betray you.
The Rick Rolling is cute, but it's getting a bit ridiculous. The word boxes you have to choose force you to say "I'm never going to let you down," which is NOT what this sentence means. "I'm never going to let you down" has nothing to do with betraying; it's about failing to achieve for someone or disappointing them, not betrayal.
Keep the Rick Roll reference as an allowed alternative if you like, but don't let it appear in the word-scramble exercise.