Does Cousin B's mother shower him in affection and kisses?

No.

You're attributing sexual behavior to a toddler, you have to understand how fucked up that is.

I have been spending the last week wrestling with my thoughts because of that being fucked up but I cannot deny what happened over and over to her daughter. This is a boy who listens to 'no' about many things and seems to understand most boundaries. Yet he was reveling in kissing and licking her everywhere, forcibly removing her clothing, and groping her as she was obviously in immense distress and objecting to his repeated behavior. What do you call that besides forceful sexual harassment? Even if you call it something else you cannot change what happened, cannot change his actions, and cannot change this being an example of males discovering that they enjoy wielding such behavior against females at such an early age. He did not learn this behavior, he learned that he likes indulging in it.