If you could write a note to your younger self, what would you say in only three words?
I had two thoughts. 1) Words can hurt. 2) Try your best.
What would your note say? 
It'll be okay 
Prepare yourself for the disappointment and don't let your hope and faith die no matter what
Leave him alone!
Please don't settle.
He's not ready.
Smile more🙈👉 it won't crack the face but it might cause some wrinkles 😛 simply always enjoy life's 😁😉
It's a game.
If I could continue, though, I would explain.
It's all a game, you play on yourself. Please don't play these games. Unless you're okay with playing them for the rest of your life. Which I don't think you are. So before you even start, you are wrong. It's no ones fault but yours for the pain you're going to feel. So no matter how boring happiness is, never think that any sort of war will make it any better.
Keep going, bud.
Don't give up
https://hellopoetry.com/words/985115/younger-self/poems/
Take a look at this, this is a lovely poem I stubled across regarding a poem to your younger self...