Well, while I know it isn't my place to say anything on this, as I certainly do not know you all too well; besides the few delightful entries I do happen upon; I hope you won't mind my attempting anyway.

The feeling of being superceded or left behind is one of the worst sentiments we as humans can experience. This is for all sorts of reasons. Sometimes, because we're not ready to let go ourselves. Other times, it's because we realize how much we've given up for something that may not have worked out. I mean, there are probably a billion reasons, and all of them are equally nagging- which may be the worst of it, the fact that its always lingering somewhere in the back of your mind. The fact that the feeling dulls with time isn't helpful at all when the wounds are still raw. But what I can tell you, knowing absolutely zilch about what you are referring to in the first place, is this--

People, things, emotions, and memories can never be lost, or abandoned, or replaced. Because, as long as there was even one moment where you held that person or thing dear, or where you felt that emotion or made that memory; then it is with you forever. It happened. And you cannot ever change its effects on you. No person can ever be replaced- not really. Even if one day you love someone, and the next day, you decide you hate them; the fact that you did love them once will always exist. And so I hope you cheer up soon, because you seem like a truly great person; very intelligent, and wonderfully creative.

While that probably wasn't helpful at all, at least you have an excellent book waiting to be read that maybe can take you mind off of things. Neil Gaiman is a God. Might also like - White Oleander (Janet Fitch), Cloud of Sparrows (Takashi Matsuoka), Lolita (Vladimir Nabokov), or A Heartbreaking Work of Staggering Genius (Dave Eggers).