Answer:
What I would do (though your mileage may vary):
1. Try to determine if my partner will never be "in love" with me, or is only not there yet;
2. If the former is definitely true, I would break it off.
3. If the situation is unclear, or if the latter is true, I would probably let it ride for a while, though I would make an effort not to get too attached to the relationship.
It's best to remember, though, that one need not spend every waking hour worrying about the inexorable drive for lifelong companionship. Living in the moment and enoying day-to-day life is a good way to spend your time; further, questions of love and being "in love" are never as clear as romance fiction and self-help books make them out to be.