The good ending is up for a bit of interpretation as to what just happened or happens after the credits roll. The three possibilities I had in mind though were:
-You died and become a ghoul alongside her.
-Your death allows you both to pass on to the afterlife together.
-She's actually just an insane ghoul and is just murdering you because that's her love language lol
There's also a third possible ending in the Steam version (which is free to download), though I don't think it will give you any more closure. The good ending is the only way you really get info on who/what Monnie is, which is partially why it's the "Good" ending. And also because being trapped in a doll for eternity is imo a worse ending than just dying hahaha