Having friends while you're growing into the person you want to be is quite possibly the hardest thing about being a young adult. You start to cycle through friends that either match your energy or tear you down, and sometimes your closest friends can be the ones dragging you behind.
It's important to realize that even some of your best friends can be draining your energy. Think about your happiness and positivity as a full cup: when you share that with people, you pour into their cup. However, if your friends hold empty cups, they'll be willing to take your whole cup in order to fill themselves up. Sometimes it's an unconscious thing where they don't even realize how energy-draining they can be.
When you stick with these friends that are consistently draining you of all you have, you end up finding yourself alone and desperate for the happiness that you once held in your cup. Your friends may realize that they're in a tough place where they're draining your energy. If you can communicate with your friends and help resolve these problems over time, then it will ultimately strengthen your friendship. Although, it doesn't always work out this way.
If you find yourself in a place where you can't see the light at the end of the tunnel with one of your friends, realize that you're allowed to distance yourself. You're allowed to remove yourself from a friendship that you personally feel is not benefitting you. Soon it comes time to realize that when you are the only person you need to sleep with at night, and if you're not happy because of someone in your life, you owe it to yourself to regain your happiness.
It doesn't mean that you care about your friends less or that you don't appreciate them anymore; it just means you have to invest in yourself. If that person is draining the energy out of you to the point it's interfering with your own growth, you owe it to yourself to distance away.