Without PLing too much, I know a couple just like this irl. She ruined his business partnership with catty BS, tanked their relationships with their entire social circle, and even made him move 1000+ miles for nebulous reasons. They are still together over twice as long as Anisa and I. If this couple does break up, it will be Anisa getting manic and genuinely thinking she could do better. Ian can never end it and here's my unprofessional opinion why.
He has put his entire self into this relationship. She is his first and only priority, and she has done everything possible to make it that way. Don't forget, she is his only real relationship, she is all he has ever known romantically, and the only thing that "isn't" falling apart in his life. He psychologically cannot end the relationship, to do so would overturn his entire purpose and sense of self. After he has ruined everything - his friendships, his pride, his appearance, his home, any hobby he might even slightly enjoy that would take focus off of her - to turn his back on the one thing "holding him together" would be too mentally devastating for his wounded mind to bear. Many such cases.