Paul: On the love level, maybe the ping-pong theory could be of help here. When you give, and nothing comes back, drop the game. No sense wasting your life, time, energy, etc. on a player who does not even return your service. Heck, if you are not even being returned an equal quality answer to your offer now, why hope you will later? Added bonus: weeds out parasites (emotional, financial, etc) in your life real quick too!
Works fine with acquaintances. Not necessarily applicable where many factors are in the balance, like deeper friendships. Use judgment.
On the other hand, depends what you can endure, too. If you still want that relationship for other reasons (acknowledging you can live without her love), stop dreaming and lower your expectations.
Bottom line: You draw the line on what you accept out of life, people and your own turf. People will respond to your incentives, whatever they are. Don’t like the status quo? Change the terms of the offer. People won’t change for you…except the ones who truly value about the relationship…except some common-sense give-and-take with these ones. They’re few but they’re worth it.