Oh yeah, I forgot about Psychedelica, have seen it mentioned and been meaning to play it but haven't gotten a chance to. I will say, though, if you're not just looking for a yandere fix, I do think Nightshade is quite a good game. The plot is actually good, all of the voice acting is fantastic, and the characters generally well-written (plus endearing side characters!) I enjoyed pretty much all the routes, either for the character or for the plot, often both. And while the yandere in Nightshade is not that extreme, they built a surprisingly good and sympathetic rationale for why he acts the way he does.
FYI, I've been playing through 7'scarlet and while the yandere is a bit more extreme and -almost- there, he doesn't quite make it for me. The bad end is bad in a different way sadly. Still gonna finish the rest of the game for the plot and completionist's sake. I've heard Monochrome Heaven has a yandere so I'll add that to my list at some point, too. Oh, and since you do have a Vita, I'll recommend Period Cube to you because it sounds like that has gotten some thumbs up's yandere-wise. Enjoy!