I've made lots of mistakes, and when I was a teenager, I lost 2 family members. I had a huge breakdown when I was 35y, and I had to built myself up again. It was a very lonely process, even with some help from therapists. I tried everything, meditation and training, but also meds (didn't help). I stopped watching the News at tv. I only listened to happy music. I looked in the mirror and gave myself credit. I used mantraes, like, "I'm a really good person. I decide who I an and what I want to do. I "broke up" with negative friends, and the few left, I helped and they helped me. I used earplugs a lot, to keep all "noise" away. I went for long walks, in the nature. And last, but most important, I started boxing!! Boxing is the best therapy I ever do. Find a thing you like to do. Maybe something you always have wanted to try. Do it, and give yourself huge compliments when achieving something!
Good luck