As far as I can tell,
tigger91, the best way to accomplish what you to do is to become an emancipated minor. Missouri, like several other states, doesn't have a statute that regulates this practice, so it's up to the courts to decide the rules for emancipation.
Missouri courts hold that a minor can be emancipated in one of three was: (1) by express parental consent, (2) by implied parental consent, or (3) by a change of the child's status in the eyes of society. The third category usually refers to a child who has married or joined the military. "However, it may also be shown when a child who is physically and mentally able to care for herself voluntarily chooses to leave the parental home and attempts to 'fight the battle of life on [her] own account.'" Assuming that your father would be willing to give his express consent to your emancipation but your mother would not, we need to determine if moving in with your boyfriend would constitute either your mother's
implied consent or if you will have "changed your status in the eyes of society."
According to
Dowell v. Dowell, a minor living in a stable, independent relationship with her boyfriend, without the custodial parent's express approval but also without her opposition, can constitute both the implied consent of the custodial parent and also the kind of "changed status" that can constitute self-emancipation for the minor.
So, if your father approves and your mother doesn't object to you moving in with your boyfriend, and you establish an independent household with him and don't depend on your parents for support, it seems that you can emancipate yourself from parental control. Once that happens, you can move wherever you want without your mother's consent.
Two further points to add: (1) although I'm an attorney, I'm not a Missouri attorney. I spent about 20 minutes trolling the internet to come up with my conclusion. If you intend to follow the plan that I've outlined above, you would be well advised to seek legal counsel; and (2) you have only asked us what your legal options are. You haven't asked us if what you are planning to do is a good idea or not. Since you haven't asked, I won't offer my own opinions on that subject. If you have any doubts about that, you may want to seek advice in our Relationships Forum.