You can not be in a relationship where the SD comes first.  You can’t spend your life chasing  the BM around the country.  You are going to give up your jobs and home. To follow SM. Just for her to move again.  If your SO what to chase BD let him. She is more important then you. You have to be number one in a relationship, 

He could legally protest her move, but he needs to act fast.

" I love him and don’t want to loose him but I feel if I move We will be living a life directed by his ex and daughter and eventually the resentment will destroy our relationship."

You already live a life directed by his ex.  You said so right here:

". Even though they have share custody his ex is always the one  dictating how, when and where things are done when it comes to his daughter."

And it sounds as if he is going one way or the other (with or without you). If you manage to 'force' him not to move, it will be him who ends up resenting you. As one comment above states, he could try and stop the removal of his daughter through the courts. He can't stop BM from moving but in some instances a court will rule the child must remain where she is already established (meaning your boyfriend would receive fulltime physical custody and it would be BM who gets solely the long distance visitation schedule of holidays and some summer).  

Are you willing for him to go to court and request his daughter remain. Are you willing to have the child 24/7 likely 80 to 85% of the time?  Doesn't sound like it as you say you struggle with the current 50/50. 

This isn't really so much about him wanting to be with BM or follow BM everytime she gets a job opportunity move. It's about his desire to be involved and to truly be a hands on parent to his daughter. He made a very conscious decision and choice to have this child in his life (she wasn't an oops baby nor was he 'trapped' blah blah). He adopted this little girl and wants to be her father and be active in her life. So yes, he very well may decide to move and follow his daughter during her minor years instead of choose to put his girlfriend ahead of the child.

Right or wrong isn't really the question. *We* here could all go on and on about how he should put his relationship with his girlfriend (who is his live-in SO) first, make her the priority et. But none of it matters as to what any of *us* say or think.  The man is going to ultimately make his own decision, and yes, he may be willing to leave you behind. 

In the event he does indeed decide he is going, you need to be prepared to make the best decision for yourself. Sometimes love isn't enough. Following him may not be the best decision for you. 

So I suppose my advice is to be sure you go into this eyes wide open and be sure you are making the decision that is in your best interest. Even if that means he goes and you lose him. You've already made it pretty clear here you know you will resent the kid if you go. You've already made it pretty clear a move is too much on your life and the way you desire to live it and where to live it. 

Review the relationship. Review your importance or lack of as a priority in his life. Keep in mind this child is six and it's many years before she ages out and is an adult (this kid might live in half a dozen more areas before she reaches eighteen). Make a list of what you view as important for you to be happy (not you and BF, but you). How did you picture your life five years from now if BM had not announced she was moving? Are you climbing and advancing in your current job, will the new area hinder this type of advancement? 

In other words, now is the time to be selfish and think of yourself. If this move is not in your best interest but he is going anyway, have the strength to let him go. Because, again, love is not enough and no man is worth selling yourself short for. 

The best of wishes for you. May you make the right decision for you. You must put yourself and your needs ahead of any man... if you don't no one else will. 

I do believe that if they're moving away, you can actually file a petition... Then she either picks losing custody, or she doesn't get to move. Ordinarily I believe it goes in favor of who is staying the the "child's norm" environment. 

I wouldn't move for her. She'll just decide to move next month when it doesn't work out, and you all shouldn't be going unemployed or disrooting yourselves on a whim of an ex.

You are correct when you say " I feel if I move We will be living a life directed by his ex and daughter and eventually the resentment will destroy our relationship."  That is exactly what is likely to happen.

This is a situation where you *need* to be selfish.  No one else in this scenario is looking out for your best interests.  Your SO is clearly thinking of himself and his daughter (and maybe his ex).  He's not considering your wants and needs.  You need to decide what is right for you, and do not allow anyone to guilt you or tell you you're being selfish, no matter what you choose.  And of course one of the considerations is the long term future of your relationship with your SO.  Do you want to be married to him?  If you do, there is no way I would move away from my job, friends and family to be with him without that commitment.  If not, you still need to consider the possibility that resentment will ultimately kill the relationship, especially with his daughter and your vastly different parenting styles.

Good luck - this is a tough one.

This is really not too different from someone that is dating someone that gets a fantastic opportunity across the country.  Either you are up for moving with him this time and potentially more in the future (for whatever reason.. kid, job etc..) or you are not.  It sounds like you like your life exactly where you are and don't see any benefit for yourself for moving.  This may be one of those situations where a long distance relationship might result.. or you might revisit this relationship and decide to find someone who is able to make big life decisions with your feelings involved.

(Is it at all possible for him to file for full custody since mom is trying to move away?).