i can only think of three other games that are similar and the rate of progress on them is .... concerning. forcefully yours has a free demo on here with a lot of content, but unfortunately the dev has been missing for a few years now. i played the demo for sterile desires when it was free and it was definitely dark (there's non-con), but the demo now costs $10 (i think it's a full chapter) and they haven't even updated it on itchio in a year and a half. i don't want to criticise anybody for how they choose to value their work, but personally, i wouldn't want to pay that much for an incomplete demo and no assurance that i'd ever even get a complete product. there's also "yours game" which also has non-con, but it's a short demo and also hasn't been updated for a while. all that to say, we're definitely being spoiled by soapinsoup xD
since you said you're looking for dark romance, i'm assuming you dont want a pure horrorporn murdersim like boyfriend to death. if, however. you're looking for a murdersim with yanderes, you can try the two games by mr fishess. courtin' cowboys is about $9 for the full game. you can see the warnings on the game page and decide if it's up your alley. if i recall correctly, two of the characters are yanderes. the other characters are either normal or just sadistic/psychos. there's a ton of content and many endings, so it's definitely worth the price imo. lovers trophy is $2 and has a lot less content, and i think only one of the two male leads is actually a yandere (the brunet guy). this game does have a demo if you wanna try it first.
if you want something EVEN DARKER to the point there's technically no romance and it's pure horror (but it's still starring a yandere), you can try wh4t 1 w0ulndt d0, which is free. there's also fall into prayer, which is super short but also more dark in overall theme.