NTA, I think it's weird your parents became so attached to her they were even having to go to therapy over her. That's just strange to me. I was in a similar situation (friend from a bad home life, parents became attached to her, lived with us for a while, but we stopped being friends) where my mom was unhealthy attached to her and I was similarly uncomfortable with them maintaining a relationship separate from me. I told my mom how I felt and she ignored my feelings about it for years and it really damaged our relationship. To me she was choosing some random girl over her own kid. No offense but like, get your own parent. Again you are NTA if they want you to visit and be a part of their lives maybe they should prioritize your feelings. They can't have it both ways.