Technically, a child cannot choose which parent to live with.  It is up to the court to make such a determination.  It will do so based on the "best interest" of the child.  Many factors are taken into consideration, most especially the mental health of the custodial parent.  Additionally, where the child is older (as in your case here), the child's preference for which parent to live with is given more weight.

What you need to do now is to make application to the court for a modification of the child custody order.  Since money seems to be an issue, contact Legal Aid for assistance; if they can't help you see if they can recommend someone who can.  You can also see if there is a law school nearby to where you live; typically the run free/low cost legal clinics that handle cases such as yours.  Finally, contact your local county bar association and see if they have a list of attorneys who volunteer to take cases "pro bono (that is for free).