I don't hate Amanda as a character. Quite the opposite, actually, I like her. She did bring a new breath into the house and she provided a storyline that got Tim Shaw to try to get revenge, which I liked. But as for her and Quentin.....
It could be argued that she and Quentin's relationship was REAL. And, in fact, I believe it was. But the question is who did he belong with, who did he TRULY love. He did love Amanda. Otherwise he wouldn't have told Angelique off at the train station, and he would have left her to kill Amanda. After all, his previous treatment of women didn't really seem to support his actions. But his character development did.
I think the reason Quentin latched on to Amanda was because she knew nothing of his past, and new nothing of her past. He was wishing that he could let everything go, including Beth's death, and start a new life with her. She had no real past before she met him, and he had a past, but one with which she was not familiar so he wouldn't be reminded of it everytime he looked at her, like he would have been with Beth. THAT is what drove their relationship, in my opinion. Quentin wanted to get away from what he had done, and Amanda was his ticket on that train.
However, I think that Quentin and Beth were soul mates, and they had true love. Their relationship is a parallel to Barnabas and Angelique's relationship. Barnabas thought he loved Ang. Q thought he loved Beth. They both left the woman, scorned them countless times, and betrayed them just as much if not more so. The difference is that Beth went away from Quentin, working for his enemy, while Angelique decided to take a more direct route to hurt her lover. They both tried revenge. They both failed. Angelique didn't always fail, but sometimes she did. Barnabas killed Angelique a LOT. And Quentin, albiet inadvertantly, backed Beth off of a cliff.
Beth followed Quentin around for the same reason that Angelique followed Barnabas. Both women TRULY LOVED their man, and they wanted nothing to do with anything else, until they were scorned. Beth and Angelique stood the test of time, trail, and error time and again, waiting for their man to realize that they were meant to be together. Angelique confessed her love for Barnabas eventually, apologizing for all that she had done before she died. Barnabas admitted to Julia that Angelique was his one true love, all this time, and he never realized it. And while some people may refuse to believe that fact, it is true. They said it in the show, so it therefore must be taken as cannon. Beth and Quentin, likewise, eventually realized that they were meant to be together. Quentin broke up with Beth, went back with her, then broke up with her again. He was attempting to make things right, to declare his love for her when he went searching for her to stop her from killing herself. Angelique prevented him from doing what he wanted. He couldn't break his vow to Angelique, because he knew what the consequences would be. And when Quentin got back into his own body eventually, he realized that Beth was the one who had suffered, that Beth was the one who had stood by him through it all, and that Beth was the one he loved.
Did he go off with Amanda? Yes. Why? Because Beth was dead, Quentin felt guilty, and moving away to New York with a woman who knew nothing of his evil deeds and who had no past herself, allowed him to attempt to forget what had happened to him at Collinwood, and to start a new life with Amanda. Quentin was widowed with Beth died, and he remarried, if you choose to see it that way.
Did he love both women? Yes. But he loved Beth more.