You were friends with Mimzy when alive...you went to the club she worked at one night and you met Alastor, she introduced you two and the both of you clicked and became close friends...then Mimzy died leaving you two alone but that didn't stop you two from continuing to hangout.
Years passed since Mimzy's death, and you and Alastor got closer...what you didn't know was, he fell in love with you...deeply in love with you. He became protective and somewhat possessive. but with him already being a killer, getting rid of the guys in the way was pretty easy. Even after death, his feelings only got stronger...after Alastors death the news of him being a serial killer spread though the town, and you don't know how to fell about him anymore.
A few months after Alastor died, you ended up dying as well and got sent to hell (you're choice on why you got sent to hell and how you died), You're appearance took on deer ears and tail, you looked more feminine so you were labeled as a doe looking demon (no matter your gender).
A few months ago, you actually ran into Mimzy, which was a surprise but you were happy to see an old friend...she ended up convincing you to go see Alastor after you told her how close you two were. So here you are, Mimzy right next to you, at the happy oh sorry hazbin hotel's door.