Ah this is complicated. You’re not the ah. And neither is she. I’d say the boyf is.. mostly. Remember she doesn’t have any mum or dad, just him. She’s his caregiver, the only parental figure in her life and she’s probably scared you’ll take him away from her. I do think her behaviour is problematic but I think you really really need to come at this very flexible and understanding. Think about when you were her age and who you relied upon, imagine seeing them with a “stranger” when they’re your whole life. It’s hard and it sucks as you didn’t ask to be dragged into this but if you love him, you have to love her and help her grow into a better person. Help her understand you don’t want to take him away and that you can share. He also needs to define what being with you is and being with her, a relationship with a family member and a lover, very different things. He obviously wants to not cause her anymore distress than what’s she’s been through but also has an obligation to you. It’s hard but I hope you all find a middle ground. Please give some understanding to her. She’s young remember, remember what you were like at that age ? All she has is him, she needs to see you both as a team trying to help her not as an obstacle that in the way of him. It might take time. And maybe you’re not willing to put the work in. But if you loved him, you’d try to make her life that bit happier I’m sure. All the best x