The movie was probably made around 2014 to 2017 and in the trailer it shows a woman who comes and stays with either a brother and sister or two very close friends(a male and a female.) They may even be cousins but it’s not My Cousin Rachel. I believe it may be British. The male starts to spend a lot of time with this new female and the sister (or friend) starts to become jealous of their relationship. It may have a weird love triangle theme to it but I can’t remember. It’s definitely more of an indie film. It takes place in more of a countryside setting, in a very large mansion like home. The sister and the other woman have long  blondish hair. I feel like the movie may be somewhat of a thriller as well. I’m sorry these aren’t very good clues but if anyone can help… it’s driving me crazy! Thanks!