Don't take anything on the internet seriously. Unless someone actually tracks down your IP/physical address and starts threatening your family/friends. Otherwise getting mad over someone who you will most likely never meet face to face that has no effect on your life is extremely redundant. Call them a fag and move on.
DO NOT replace your social interactions with the internet. The internet should be used to supplement a already existing social life. However it is better than nothing if you are at a low point in life.
Always look to improve something. I don't care what it is, as long as its something other than getting achievements in vidya. Learn something, cook something new, talk to someone new, workout, improve your looks etc. Do not get stuck in a rut where the only thing you do is eat, work, and sleep. If you do at the very least try to change something to make you a better person every day. "Rome wasn't built in a day" is a valid saying to me.
Learn to trust people. Yes people will try to manipulate you, or act like some sort of asshole to climb over you, but most people aren't like that or are worried that's what you're doing to them. Keep healthy suspicions.
Your body should be treated better than any temple. To fall to some vices like occasional drug use (i'm talking minor shit like cigs and alcohol) is human, but for the love of god please at least go for a fucking walk. Especially if you are already unhealthy. Eat better, even if you add just a couple of servings of fruits to your diet.
Relationships, even if they seem like they are going well sometimes don't work out. This is true from family to romantic. But especially for romantic do not think that person is the only one with the capacity to love and "complete" you.