The word that no one dares to speak of because it's too painful, brings back bad memories or it's the word that if you speak it, makes you sound weak. Rejection is inevitable. You will get left out of things, feel lonely and like you're not worth anything. I'm not trying to be negative, but I'm pointing out that even in the midst of all this rejection you've been feeling, God was always right there with you.
If you have friends that exclude you, a boyfriend that once longed for you is now rejecting you or even if your family makes you feel lonely and you think that no one likes you, God likes you. He liked you so much that He sent his one and only son to die for you. He knows that you're worth it and is just waiting for you to run and seek Him -- go ahead and run to Him. Even if all of your friends ditched you and you feel so lonely, turn to God -- turn to Him because He will forever love you and never leave you.
Deuteronomy 31:6 says this - "Be strong and courageous. Do not be afraid or terrified because of them, for the Lord your God goes with you; he will never leave you nor forsake you."
It doesn't matter what everyone else thinks of you because their opinion doesn't matter. His opinion is the only one you should care about and you might say that you want to "get revenge" on the people who have excluded you from things, but God wants you to love your enemies. You have a God who loves you so much, and in any situation, you can walk away knowing that.
I've been left out countless numbers of times, (and it still happens today) and every single time this happened I would go home and wonder why. Just why. Why me? Why now? What am I doing wrong? -- I can't keep doing that, because I've realized that even though other people aren't there for me, God was there the whole time just waiting for me. He wants us to have a thirst for Him and for us to continually seek Him. He is patiently waiting.
I know that getting left out and feeling lonely sucks, but I've learned that I have to focus on God and that He will take care of me and not my situation.