I have joint custody but my ex wants to move out of state

My ex and I were never married but upon splitting up we established his paternity and agreed to joint physical and legal custody. We both felt that it was in the best interest of our daughter that a close continuing parent and child relationship with both parents be established and maintained. After our split, I have since married and now have 4 children. My ex has never married or had any more children, so essentially, when she is with him, she is an only child. We lived in Michigan but six years ago my ex asked if we could all move to Georgia. I agreed and my husband, me, my four children and my ex all moved to Georgia to better our lives. Two years later, my husband and I fell on hard times and asked to move back to Michigan. My ex refused and so we stayed. For the following four years, my husband and I have settled well in Georgia and now have close ties to the community, schools and work ( my husband supports the family while I am a devoted stay at home mom). Today my ex served me with papers for a modification of custody wherein he expresses his desire to move to back to Michigan with our daughter. My daughter (now 12 yrs. old) says she wants to move back to Michigan too. She mistakenly thinks that if she goes back with her dad that I will have to follow. I have already uprooted my family once for him and then stayed when he refused to go back before. I do not want to put my family through another huge move. Continuity and stability are important for them. My other children should not have to be uprooted again due to his whims but neither should they lose the chance of a lasting relationship with their sister. I couldn't bear to have my daughter so far away. As a stay at home mom, I devote all of my time to my children. His reason for moving are that he's lonely here and he possibly has a better job opportunity back in Michigan. Would a judge really side in favor of him moving when we have always striven to co parent equally. Wouldn't maintaining the bonds she has with her mother, her siblings and stepfather be more in the best interest of the child especially since her father and mother only live minutes from each other right now. Would a judge grant him custody, knowing he'd be moving out of state far away from the rest of her family? He is a great father and other than these proceedings I have nothing disparaging to say about him and neither does he of me. What would he have to do to prove that it is in her best interest to be separated from her family? He has stated that he won't move without her. Wouldn't he have to prove me an unfit mother in order to change the custody that we already have? Our parenting plan is filed in the Georgia court system. Any help or advice would appreciated. I have already retained an attorney, did that the second I was served today, obviously, but I'm just trying to see how worried I should be. I'm panicking. My other three children are terrified of losing their sister. She doesn't get back from summer vacation until Saturday. She is 12 years old but doesn't understand the ramifications of what is happening so how could she be allowed to make such a drastic decision based on false hopes that we'd all go back to Michigan and live happily ever after. She doesn't understand how devastating this is to us. Of course I want her to be happy but I have to consider the best interests of all of my children, not just her. Will the judge consider them in his decision or just her?

You have an attorney. Ask them. Anything is possible and yes, he could be granted custody to take her to Michigan and have visitation with you. It won't be up to the kid, but the judge certainly may ask her preference and take that under advisement. Unless you lied to her, she is old enough to comprehend that you aren't moving as well. Your kids won't really figure much into the equation. The judge isn't going to rule based on a younger sibling's preference for where the girl should live.