I'm so sorry for your struggles, Little Cat and gayleggg
I understand how you feel, and I tend to really hide things as well. And for me, in order to hide things, I transit myself into another reality just to blend in with others, like how actors do when they rehearse a scene or when they're performing it. The only person who knows about this in real life is my friend, and with him I don't hide things at all, and all I find is me just being completely silent and sad. Comparing things to how it was before telling my friend, I was always talking and laughing, but he soon began to see a pattern to everything and told me to admit what I'm feeling, which I did eventually, but even then I denied it and said that nothing is wrong at all.
And I don't know, but do you ever feel "used to it"? As in, you've been feeling this way for a long time that it became a routine and that you've forgotten what happiness is (whether you have depression or not)?