Yes, I'm experiencing the most extreme case of that right now! If your friends are ditching you, then focus on other people or events. Get involved in social events. Find something you enjoy doing and get to know new people. Don't let one group of people determine how you feel. Start focusing on yourself instead of their actions and you will start feeling better.
If you are alone for a long time, the loneliness will get to you, and its very possible for you to get depressed. But the good thing is, you no longer have those toxic friends, and you can go out and make some good and supportive ones. I know friends don't hang from friend-trees in friend-land, but still, get engaged in many activities, join many groups and all. You will find lots of people who are similar to you. Good luck....and for the time being,I suggest you read a good book. :)
Yes, we're social--even the introverts like me need some kind of contact with another person or animal. But as a person who didn't get friends until High School, that person doesn't need to be a friend. You can enjoy a book in a library, or engage in a conversation with someone you've never talked to in a class. Also, joining clubs/groups like violet suggests is the best idea! The ones who left you were never your friends. Go find people that add sunshine to your life. My sisters became my best friends, even with friends of my own, they're my best and always will be my number one friends.