Depression is most certainly not a choice, but you already know this. Sorry you have to deal with that.
I think most people suffer with depression at some stage of their lives but knowing this does nothing to keep those horrible dark emotionless numb feelings at bay or help you feel better, still It's kinda comforting to know you're not alone, especially on this forum, most here will know exactly how you're feeling, including myself.
If you're having thoughts of suicide, I would definitely urge you to get some professional help, or at least talk to family and friends even thou you feel as though they wont understand.
I know you're in a dark place at the moment but that's exactly what this is, a moment, and moments pass, no one knows how long you'll continue to feel this way, just know at some point there will be a return to feeling happy, content, motivated and alive.
You mentioned that when you're around people you act as if nothings wrong, that's fortitude! And it's a virtue of strength and personality that's rare in people.
It's such a thin line from being on top of the world to being bang at the bottom, just hang in there, focus on the things you enjoy or find something new that's totally out of character for you, sometimes we find motivation on new ground when we least expect it. Meanwhile make a fist, grind on and soldier forward.
Feel free to message me if you want to chat.
Daks x