Allegiances shift in response to Edwards marriage. He has alienated both his brothers and his potential allies in France, as well as his supporter Warwick, by choosing to marry someone he liked rather than someone politically expedient, like Lady Bona.
Edwards marriage mistake is similar to Henrys errors in marrying Margaret. Many were dissatisfied that Henry chose to marry Margaret rather than a richer, more important relative of the king of France. And Margarets ambition has been repeatedly blamed for Henrys weakness as a king. But now Edward, not learning from the mistakes of Henry, chooses to marry Lady Gray without consulting his brothers, allies, or advisors, and everyone will turn against him. Clearly marriage arrangements were important ways of aligning ones allies and enemies, and Edward should have undertaken his marriage with greater care.