I feel like I'm losing interest in my wife and I'm falling in love with her sister and I can't help it.
Is that really true? How are you going to approach the situation?
It is a very complicated case and I don't wish to discuss it with you.
I can see how you're losing interest and starting to fall in love with your wife's sister. You should try to work on your relationship with your wife to attempt to rekindle your love, communicating issues to your wife can help fix any issues in your relationship. Continuing to have these feelings for her sister without communicating anything can result in you losing them both.
I don't want to lose my wife, but I want to blame her for everything, maybe I could blame her for enticing me and seducing me to also fall in love with her sister.
I think it would be smarter to not try to think that way, and attempt to reconcile your relationship with her. You can choose to be honest which can hurt a lot, or improve yourself and maintain your distance from her sister. Your wife deserves a good marriage.