I agree with glok. You need to protect your marriage, first and foremost. Your sister may very well be jealous of your relationship with your wife, in which case, you are all the more justified in protecting that relationship.

It's very sad what happened to your sister, but, by continuing to be aggressive towards your wife, she is not considering your well-being. She really should understand your predicament.

Ultimately, you have to come home to your wife. So, let that fact be your guiding light