>>20596540
Another good option would be to lead Remi on with very occasional praise or gifts, so even though she's unhappy, she'll always have a tiny bit of hope that her relationship will get better. Then, impregnate Flandre and break up with Remilia, saying that all of this is her fault because she couldn't satisfy you, and that you're going to marry Flandre. After that, move out with Flan and send Remi tons of pictures of your honeymoon, specially pictures of you two having sex. And the killing blow would be to send pictures of you, Flandre and your child being a loving and happy family.
This will ensure that Remi develops trust and self-esteem issues and can never be in a relationship again, becoming a lonely cat lady.