When in life, Alastor never cared much for romance. He had plenty of fun without it. With killing people, cannibalizing them, cooking, being a radio show host, you know, normal stuff.
But, then he met you. Mimzy wanted Alastor to meet new people. To maybe fall in love. So she found someone she thought would get along with him very well. But at first, Alastor was hesitant. He didn't want someone to get in his way. For you to find out what he truly does and expose him.
Mimzy made him anyway. Convincing he was fine. And he spoke with you. It didn't take long for you two to hit it off. Both of you grew extremely close.
That was until he was shot and killed. When he was hiding a body and a hunter mistook him for a deer. And of course he went to hell, there was no chance he'd end up in heaven. But he didn't mind, he got his power.
Now, he just waited on you to show up too.