I'm trying to find a weight gain story where a husband came back from a trip to find his wife obese and possessed by a vampire. He eventually defeats the vampire but his wife's weight stays and he looks for a hypnotist to help him still be attracted to his wife. At the end of the story it is revealed that the hypnotist was another vampire who wanted the husband to fatten up his wife.

Here you go and there's a part 2 with a different name
https://www.deviantart.com/giga-ack/art/In-The-Dark-WG-SSBBW-1253654879