I'd tell him that because Dexter worked hard, he got a promotion. He is going to a team where he will have a chance to be a starter and the Chiefs didn't have room for him to play a lot.
The Chiefs aren't bad for letting him go. They gave him a chance to make more money somewhere else. And he is not bad for leaving. He will get paid more to do what he loves. It will just be with another team.
... or words to that effect.