I just finished all translated chapters in 2 nights and now I need more. I don't usually go for horror but this mix of mystery/horror/romance worked for me. I would love to find something similar, preferably with a happy ending (or at least nothing too tragic)

I'm trying to narrow down what I liked about this so it makes suggestions easier...I loved the art, I liked that there was a small cast and the main characters pulled focus, the focus was on them and their story and the mystery that surrounded them. It didn't feel dragged out or bogged down by a large side cast. I liked that the romance was a large element but it was ... woven into the mystery sort of? So it didn't pull focus from horror parts but worked along side it? I'm not sure if any of that makes suggestions easier >.>

I literally just read season 1 on taptastic and I don't think I've read anything similar to it. I finished it all in five hours and now I want to read the second season so bad ahah.

Things that don't completely match up with what you said but you might like are:
The Pale Horse the cast is larger but it has both gorgeous art and mystery
Melo Holic it gets more messed up as it goes along. The romance tag is deceptive.
Dokuhime I can never recommend this one enough...

These might not have the happy ending you want

I've come across Melo Holic before but the comments kind of threw me off. The other two are new to though so I'll be sure to check those out, thanks!