Mainly, similar to what I tell my teens, focus on people that make you feel good, not the ones who make you feel terrible.
Build relationships, mostly with those who you feel good around, they're important - all of them, including the platonic/affectionately platonic/casual ones. Work on connecting genuinely, learning what you like in people and in relationships rather than overthinking what things need to mean or go a certain way or defining yourself by them.
More personal to my specific teen situation: Affection doesn't always mean something major and that's not a bad thing. You can enjoy affection without the pressure of thinking it proves anything. It proves nothing about your worth to accept or reject it or if they want or don't want it, it proves nothing about how the other person feels or even how you feel about them, it proves nothing about your mother's opinions of anything. You can enjoy it and company just for the fun of it, just don't let it get in the way of your goals or do it if it feels terrible.
Some people think saying you like them/think they're cute/similar and the other person agreeing is the same as agreeing to go exclusive & get real rude if you don't agree. Some people will push to go exclusive but leave you dangling. Check for these thing, you'll be happier with more flexible, relaxed people who can communicate well.
Less overthinking people you plan to leave and just enjoy things as they are for the time. When your driving force is moving far away, bit daft to also think connections and relationships only matter if they last longer than that or have some sort of public commitment to them. Besides, pretty much every guy you went to high school with goes bald before 30 (that one stops being a flexible relaxed guy and becomes way more uptight in a vegan, distance cycling, politically child-free and beyond way), many of the once hot girls end up copies of their mothers you didn't like, few of them make it more than a couple hours from your hometown (my idea of a nightmare) and you end up married in another country less than 6 months after you graduate. It all works out, you're fine, enjoy things, maybe keep sending more emails after you leave, but in the long run, they will lose their importance.