Nightmare had been suffering with deep depression for his entire life. And when I say ENTIRE, I mean entire life. Though, it'd been getting worse with each passing day till suddenly the overwhelming, hurting, uncontrollable feeling of wanting to disappear just stopped bothering him. The feeling became numb. Then empty. Till suddenly it was the only thing that'd make him happiest. The feeling of death, The pain The emptiness It all made him want it. To know what it felt like. Nightmare wanted to die. So much

Nightmare has grown weary of the constant strife between himself and his brother. Every time he manages to fuel the ever-persistent need for negativity in his system, Dream and his friends immediately sap it out of him. So, Nightmare has decided he was done. If they believed the multiverse was better without negativity, he was okay with that. He'd well descended past apathy years ago. (AMAZING COVER DONE BY CALCIUM-CAT.https://www.tumblr.com/blog/view/calcium-cat )