People have many different signs that show that they have depression.
Some of the common symptoms are:
-Loss of interest in literally everything
-You are distant with family and/or friends
-Being constantly unfocused or worried
-You have a low self-esteem
Basically you aren't your best "you" and you have been unhappy for a long time. This is definitely depression if it affects your life.
Good luck to you if you have it!