This had so much potential, but the ending just takes all of that and throws it right in the trash.

If you read everything except the last chapter it's actually quite good. The premise is interesting and the delivery for the first 13 chapters is well done. Everything is very clear and doesn't cause any confusion, there's some nice jokes, and you also get those messy situations that I know you want to see from this type of series but don't want to admit. But then the ending comes and just ruins the whole story. The ending isn't interesting at all and just negates all of the hard work everyone's been doing in the past 13 chapters.

TLDR; Bad end.