It's okay to be sad. People will tell you: "You can't be sad, there are people who have it worse." This is true, But it is okay to be sad.
Sometimes the weight of living becomes too much. It is okay to be sad. You can't appreciate happiness if you are never sad.
If you want to cry yourself to sleep because you Cannot deal with the world at the moment, That is okay. It will get better, But for the moment, It is okay to be sad.