I don't get it

So now I'm just sitting here, crying my eyes out, wondering why feeling like these exist.
I don't wanna be here, I don't wanna cry, I don't want to feel sad, I want to be happy. Where is that goddamn switch in my brain? Why am I not happy? How is that possible when I have all I ever wished for - and even better? I have friends, I have a home, I can learn things, I can listen to music, I have a boyfriend who is better than I could have imagined, I have parents who take care of me. I have everything I need to be happy so what the hell is wrong with me? Where the hell did it go wrong in my brain? Why is this happening? Why is it possible for people to feel like this?