Let it go. They’re going to make really stupid choices. I drank AND smoked in high school. We all go through it. They need to be able to trust you and rely on you. They’re navigating the world and they need a safe harbor. Be that safe harbor. It’s more important than fighting over stupid behavior. Let them know you don’t approve - sure, but fighting over stupid stuff is just going to make you both bitter.
When making decisions remember HALT: are you hungry, angry, lonely or tired? (Or ecstatic) Give yourself time to be in a good place. Ask yourself if you’re choosing something because it’s going to bring you closer to being as authentically yourself or are you trying to meet someone else’s expectations? This is not to say you won’t need to compromise and put others first (spouse/ family.) That happens a lot in marriage. No, I mean ask yourself if you’re trying to prove something or are you being true to yourself. Hope that helps.
On grief: CS Lewis said somewhere that it isn’t just that his friend died, it’s that the part of him that only his friend could bring out would never be brought out again.
One regret I have is how sure I was that I was in the right. Looking back I can see now that there were plenty of times when I was the a-hole. I wish I had been able to be circumspect.
Date all kinds but marry someone who loves you for who you are, with whom you feel most yourself. Someone who will encourage you to grow more into the person you want to be. (And be good at encouraging them to do same.) Never fear or stifle each other’s growth. Celebrate it. Support it. Encourage it.
Teach your pets they can trust you. Take care of them. Treat them with tenderness. Teach them how to behave. (Unless it's a cat. You can't teach cats anything.)