It is down to him to work on a relationship that meets her needs and boundaries. She’s putting in a boundary of distance and the more he disrespects it, the further away he will push her.
This is not something you can fix, so no CAMHS or mum or dad or relative involvement, no court can make everyone happy in this situation. He is going to lose time with his daughter and whether that’s his fault for the past, her feelings now, her loyalties or wherever it is, it is just the situation now and all that needs to be focused on is ‘what happens now’ and that she is reassured she is mature enough to make this decision and be respected for it.
It’s going to be a new normal for him to get used to. And he’s not going to like it. This situation makes people feel very angry and almost inferior and they look for someone else to blame or a reason why. Often children can’t really explain why they feel a certain way, they just do. It won’t just be the new situation, or the OW, it will possibly also be his lack of awareness about how to talk to her and not really connecting with her. If you were 14 would you want to spend 2 days with someone who didn’t really know much about you, your interests or anything and you couldn’t speak openly about your real feelings? She might not be allowed or comfortable to air her real feelings to him, so it’s easier to pull away.
I can tell from my DD’s facial expression or body language how she is feeling, her dad cannot do that they just don’t have that connection.
Girls can feel very uncomfortable around a dad they aren’t close to, I know my DD started to feel very anxious about periods and showering at her dads and this was a contributing factor to her decision, but she didn’t want to tell him this so withdrew. She did not feel at all comfortable with discussing any of that with him, sad as that is. I’m not superior or better than him, I have made a point of putting my DC first and knowing them inside out as best I can and trying to adapt with them, acknowledge their feelings and work through them with them and not just expect them to slot into my life