Depression

I get so depressed when my boyfriend leaves for work. I can't do anything right. I break down. I feel like I shouldn't exist. Before we dated I was suicidal and whenever he leaves I get suicidal again and I just don't want to exist anymore. Right now I feel so numb and worthless I just want to die. Nothing is stopping me from killing myself except him. I can't function without him. He tells me to be happy but how am I supposed to do that when the one thing that brings me happiness isn't even with me?