I think it was more comparing Obito to his own attitude and view of life when he was an old man. It was way different then. His hatred had turned into some sort of depression that he gave to Obito by telling him the world is full of war and so shitty it has to be changed.
Yes I agree that he meant that about Obito's attitude and goals, not personality.
Btw, the way he loved his brother and couldn't get over his death, I don't think a girlfriend would have meant anything to him at this point. He was too broken to worry about such things. It would seriously ruin the character.
Um, we don't really know. All we really heard was Obito's version, with a comment by Hashirama. Madara seemed like a fairly unpleasant person even as a kid, in the last episode. I think he actually caused his brother's death by either stealing his eyes or conning him to donate them. Desiring power to the point of sacrificing the brother you love to get it, that definitely would have put one on the evil path....
Besides, he was probably married: Obito referred to him as his "ancestor" in his flashback to his meeting with the old Madara, and Sasuke is probably also related or even a descendant.