The behaviour of Darnley meant that Mary refused him the crown matrimonial, which would have given him the power and authority of a King, and inheritance of the throne if she died prematurely.

No, Mary, Queen of Scots, never granted Lord Darnley the Crown Matrimonial, which was a major source of their marital strife. The Crown Matrimonial would have made Darnley a co-sovereign of Scotland with equal power to Mary and the right to keep the throne if she died without an heir. While Mary gave him the title of "King of Scotland" shortly after their marriage in 1565, it was largely ceremonial. Darnley, fueled by ambition and the advice of the Protestant lords, repeatedly demanded the full legal status of the Crown Matrimonial. Mary grew increasingly wary of his erratic behavior, arrogance, and lack of political skill, leading her to steadfastly refuse his request. This refusal alienated Darnley and drove him to participate in the brutal murder of Mary’s secretary, David Rizzio, in 1566—an act intended to intimidate Mary into granting him the power he so desperately craved but never officially received.