I think that the problem with finding "true love" is that people want the fairytale, but no one lives "happily ever after". There are always problems, and there are always lulls, and people are always taken for granted as time goes on. None of that has to do with love.. I used to say that love is not a feeling.. it is a verb. Love is an action that we have to do everyday. I am a huge Doctor Who fan, and in an episode he states that "Love is a promise" and I feel that too.
So, simply put... Yes, anyone can change... if they choose to do so. But No.. no one is going to change FOR someone else. People only change FOR themselves, and you need to let them do that on their own.