Oh I forgot the part where you said reincarnated as a villainess…but here the fl has a cheating husband and she builds a theatre https://www.mangago.zone/read-manga/for_those_of_you_for_whom_regret_is_a_luxury/
the fl has red hair and the mistress has i forgot but i think its brown or blonde
Can you explain a bit more? Is the cheating man an emperor, a duke? Something else you can say about the plot?
it's a duke, with black hair the duke is also an owner of theater, that's why he got mad to the fl after he found out that the fl also built a theater
its historical manhwa where the fl reincarnated as a villainess, the fl has a husband who is a cheater. and the fl build a theater