Where’s Ned’s Survival guide for times like this

I’m 19 years old and I just got out of a 3 month relationship which also happened to be my first relationship. Things were so good at first but then he started talking marriage before we even hit the 3 month mark and it scared me. I got distant and he got possessive and manipulative and controlling... I finally gathered up the courage to breakup with him and even though I feel much lighter and freer without him constantly hovering over me, I feel lost and sad. How do I survive things like this??