How To Not Be Depressed
It's not healthy to stay indoors all of the time. Your mind works better with fresh air and nature can help inspire creativity. If, for whatever reason, you can't go outside then open a window and be near it. The fresh air will do you good.
You remember when you were a kid and you would get really excited when another kid wanted to play with you? Same thing here. As humans, we are very relationship-minded. We need social interaction so don't avoid your loved ones. Even if you think you'd rather be alone, you'll be much happier with the company.
"If I'd only done this..."
"If only I'd been nicer to her..."
"If only I'd worked a little bit harder!"
Look, we've all been there. You could play the "if only" game until you're a cranky old man but if you spend so much time feeling sorry about what could have been then how can you ever move forward? You have a whole life ahead of you, but you can't live it if you're too busy looking over your shoulder.