If your daughter is asking to come and live with you full time, I would listen to her. She may only be 8, but if you both ignore her she will possibly lose trust in you to help her when she asks you to and may feel no-one is listening to her.
It's very hard for a child to go between two homes permanently. I know someone who was in a similar position when their daughter was nearly 10. Her school work and relationships with family and friends were going downhill rapidly and it took a while for her to tell her Mum and Dad why. She thought they wouldn't understand or think she was old enough to make the choice for herself.
Within a couple of weeks of moving to her Mum's she was back to her old self. She spends every second weekend - Friday to Sunday - with her Dad, and also has dinner with him every Tuesday and Thursday, then he takes her home.
As usual it took longer for the adults to adjust, but they realised that they had to put what their daughter wanted first and everything has worked out well for all of them.
Not sure about that, once you've started on that road it can make things difficult.... the people I know sorted it out quickly between themselves without any difficulties. Would you be able to get some free advice from a lawyer regarding your position ? I'm not sure where you live, but in the UK a lot of law firms will give an initial consultation free, which would maybe give you an idea of your legal position.
perhaps if you asked your daughter to write a letter to her father explaining why she would like to live with you better than him he would see that she is capable of making (or not making) this decision herself. It also takes some of the pressure off of you in that it won't seem like you're trying to bribe her.
The suggestion that the other person left may also be worth considering. Her father may be unwilling to be a "weekend father", but if it's made clear to him that he will still have regular weekday visitation as well, he may be less hostile.
