Henry VIII really could marry Catherine because that is the exact case of Yibum. Arthur had married Catherine but did not leave any children. So Henry was obligated to marry her. He did not need the excuse that the marriage had not been consummated. And when he wanted to annul it, he did not understand the verse that marrying one's brother's wife is a an "erva" [prohibition of the sex because of close family relations.]because that verse refers to a case where the brother has had children.
I should add that the sexual acts of Leviticus 18 are not all because of family relations. But all are under the category of "erva". E.g., a nida is an erva. [That is a woman who has seen blood. She is forbidden because of Erva until she dips herself into a natural body of water like a river or sea or spring. All the "arayot" are ae guilty of a " Karet offence, but not all get the death penalty. Nida is an example of that. It is Karet but not a death penalty. A homosexual relation is also an "erva but does get the death penalty.]"
