Responses
I would likely to rec you this manhwa if you have not read it yet: https://www.mangago.zone/read-manga/sweet_trap/
It is not similar to the manga you are looking for, but it has a sister and brother conflict
someone actually helped me find it! it's https://www.mangago.zone/read-manga/natura_turaly/
i need help finding a manga; the mc (m) has a twin (f) and the two are inseparable. they go everywhere together, do everything together, etc. well at one point a guy joins them and the mc ends up liking him. the guy likes him too, so it's all good but it begins to crack the relationship between the twins because they will no longer be together forever. it turns out that the other twin also liked the guy, but gave him up to her brother(?)