No one will ever love you the way they "should." I think this is why so many people are so miserable in their relationships. We put "shoulds" onto other people and then get all upset when our expectations aren't met.
People will let you down, not because they are selfish and bad, but because they are human. They will think about themselves and do what is best for them most of the time, even if it doesn't look like that's what they're doing. Sometimes they will just make poor decisions and choices. In order to really love, I think we have to allow for that. We are our own responsibility. We might love someone and share with them for a while, but ultimately, our happiness is on US.
I have loved so many people who didn't love me back the way I thought they should have. And I have been loved and been incapable of returning the love the way someone else thought I should. In some ways, I think it hurt more to be the one who wasn't loving enough.