I think in the majority of cases, it's best not to go too overboard on telling a YF how much of a difference he's made in your life. They usually aren't mature enough to understand or be able to handle that well. You may see it as an affirmation on how much he means to you, but he may see it more as a burden. Young people generally aren't accustommed to having such a great impact on someone else's life. Being able to greatly influence someone's life in a positive way carries with it the possiblity to greatly influence someone's life in a negative way. And a YF usually can't handle something like that. Better to just tell them and show them how much you love them, and keep the info about how much of a difference they've made in your life or how they "saved" you for a time when they're older.

Dakota