Jealousy is a tool of control in relationships, and often escalates or is accompanied by emotional, physical, and other forms of abuse. Being jealous of someone's therapist is an extreme form of jealousy, as the potential for a sexual relationship to develop is at least minimal, and because the partner is going to therapy for help, not to take away from the relationship or the partner. It's anyone's choice if they don't want to go to therapy, but to try to stop your partner from going through guilt or manipulation, that's control. And probably abuse. Continue in such a relationship with OPEN eyes, especially because you've seen jealousy have bad effects before.