Much of the time our love for someone comes from how well they are able to satisfy our needs and desires. Once they stop fulfilling those needs and desires, we start resenting them. We are very rarely unselfish in love. Love is coexisting, not because you want to or don't want to, but because it is in tune with the natural harmony of the universe to do so. We only need someone when we are not fully aware of ourselves, when we don't see how accepting all of life is of us and how every moment of our lives shows us our interconnectedness with all of life. When you see this, "you" or your ego is no longer there and you are aware of the constant love that is recreating all of life moment to moment. THat is why they say that God is love. Only then can you have a honest and true relationship with someone, only then do you not impose yourself on them anymore. You are free together and share everything together because you know nothing is your own.
If you want to read more about spiritual love, go to thetruthisalie dot com and click on the entry called "The Present". I recently found it online and it is redefining how I think about relationships and all of life. It is also free so that is not a problem.
Also another book that talks about what true love is; "The Pussy" by Kill Gib. check it out !