My neighbor's free will is completely separate from mine, just like his life or his body. We were made to help each other, but our minds each have their own space. Otherwise, another person's wickedness could become my evil. God wouldn't want that. He wouldn't want another person to have the power to make me unhappy. Nothing can do that except my own wickedness.
Unto my free-will my neighbour's free-will, whoever he be, (as his life, or his bode), is altogether indifferent. For though we are all made one for another, yet have our minds and understandings each of them their own proper and limited jurisdiction. For else another man's wickedness might be my evil which God would not have, that it might not be in another man's power to make me unhappy: which nothing now can do but mine own wickedness.