You are generalizing from the single datapoint you had with your wife. Many women are not finished with sexual desire by their 50's. Avoid overgeneralizations.

You should not be committed to your wife. There are valid reasons not to rush into a relationship with this woman who is admittedly very forward, but staying committed to your wife should not be one of them. You have not had a sexual relationship with your wife for 4 years. Your wife attempted on multiple occasions to encourage you to have sexual relationships with other women. Your wife does not love you. Your wife initiated divorce conversations and is going to burn her wedding photos. She is in the habit of sending you nasty texts. There is absolutely no reason to say committed to her. Discuss this odd desire to stay committed to her with your therapist.