He kept Serina for revenge ? LOL He kept her for sex.

No kidding. He was more honest with Selina when he said it was for his own ego. He just wanted the sex and to know that she was still dependent on him in some way, shape or form. And I also don't buy that he had "known" that Donna was "meant" for him from the moment he saw her. Nope. Only thing I do buy is that both he and his brother are/were selfish assholes, who wouldn't truly understand love if their lives depended on it.