I spent the entirety of my youth as a complete loner.
I burnt myself out of video games by College (Did I mention I was morbidly obese /obese)
I figured the thing I was missing the most was a girl.
When I found one that would talk to me, I fell desperately in love in a codependent way (Lost some weight Obese/overweight),
She lost attraction to me because of my undeveloped or complete lack of independence around her, as her desire for me waned, my desire for her grew in the most desperate of ways.
Having effectively friend zoned me and I desperately needing sex, we came into conflict, but my inability to recognize that my neediness had damaged her respect for me, and my door mat behavior, had turned me into convenient poison container for her. ( probably in the slightly obese/over weight category around this time)
Eventually it broke me down, and as I headed toward a full on collapse, I told her I began to feel suicidal, this caused a quick explosion of events and she cut all ties to me.
For the next year and a half I battled depression, I reached out to a former bully who had contacted me during college to make amends. He actually talked me down at one point, and I started hanging out with him and his friends, people I new from High School. I woke up completely depressed every day, the mornings were the worst, sleeping was my only reprieve.
It wasn't that I wanted to die as much as I found it impossible to handle the emotions as they hit me and the desire to silence them was so great. I had to move back in with my parents, and being a generally independent person was not happy about that. As I started to hang out with these people from High School, I started being introduced and reintroduced to people, experienced drug culture, beer pong, sports/fantasy leagues, popular shows, trivia nights at the bar. All sorts of things that I would find a reason to not participate in otherwise. I went to their houses for parties, and I started hitting up the gym. and kept trying to meet girls, almost always ending in failure in one way or another.
What snapped my depression was a combination of these events but especially, meeting and interacting with people, getting involved with activities, especially those that took me out of my comfort zone, physically demanding activity, improved diet, and ultimately meeting a girl and getting laid.
After that I found employment, moved out, I didn't get laid much, but more than none. Lost that job (contract expired), did a program with the military to try and get in as an Officer, got into good /athletic shape but decided not to continue , got another job, found a gym that did BJJ, fell in love with the art. Applied to, and got a much better position, moved to a new place and a more serious BJJ gym, got into great shape / athlete shape, got into a relationship, grew my circle of friends, started hiking mountains, left my last relationship after two years, got a promotion, and started looking for a girl again.
I don't think one thing will snap your depression, but I think you need to put yourself in uncomfortable situations that test your character so that you can grow, which will allow you more weapons to combat adversities.