Nothing terribly deep or fascinating, but just the fact that V had looked up to Sebastian for his entire life up till then, and felt the loss of not knowing his brother. The loss of a sibling companion for life so to speak. I'm an only child, but I've seen how close some siblings are, my father and his for instance. Cut one, cut them all.
Perhaps thats why V wanted to take Sebastian into himself so to speak, absorb his life and continue it as his own. The life that Sebastian could not live for himself. V would in essence live it
for him.
And yes it
was important to have the record set straight, and not let that slimy little man have the last say. You know I couldn't help but think of Field's bio of VN, it makes me wonder if the reason VN and Vera were so open with Boyd, was in fact to set the record straight.