Someone made mention of this one already, and I'm not sure if you ended up trying it, but I just wanted to give it further recommendation for anyone who comes across this thread:
YOU and ME and HER
https://f95zone.to/threads/you-and-me-and-her-a-love-story-v1-00-nitroplus-jast-usa.51639/
If you haven't played it, go into it blind. Once you reach the point of yandere, the tone shift is instant and it becomes wild. Game itself does a lot of 3rd wall breaking (It's speculated as being a primary influence when it came to aspects of DDLC's creation) It's also rather long, fair amount of routes with a fair few bad ends. Also, while the game is tagged with NTR (Which I know can be a turn off for some), it is to my recollection limited to specific avoidable routes.
All that said it's an incredible VN with some of the best yandere stuff I've ever seen, definitely would recommend giving it a go.
Considering you mentioned Teaching Feeling:
Butterfly Affection
https://f95zone.to/threads/butterfly-affection-v1-0-3-ray-kbys.26071/
Game itself is a lot more straightforward, is focused on aspects of a monster turned human slowly developing an obsession with your character, and is quite short. (If you enjoy that developer's stuff or the general theme of the above recommendation, although this one seems to be somewhat stuck in developer hell:
https://f95zone.to/threads/determinable-unstable-v0-2-0-pilot-ray-kbys.33552/)
Something else you may want to try, although I have little knowledge of how much yandere is present, but from what I understand there are at least a few yandere endings associated with it:
White Wings
https://f95zone.to/threads/white-wings-final-pureworks-japan.58787/