I'm currently developing one now, although I must admit the details are giving me fits. A young scientist is followed throughout his career, from his thesis to his most productive years in research, and finally to a comfortable but undistinguished semi-retirement as a college department administrator. He meets, falls in love with, and loses three women during this arc, not realizing they are actually the same woman, a time traveler who periodically appears and seeks him out because she loves him too.

The protagonist makes these encounters during the spring, summer and fall of his life, but his lover, having control of the temporal travel process, does not synchronize her life with his. He meets her as a mature woman when he is a graduate student, a young girl when he is an established researcher, and finally, both meet in their maturity, finally coming together, but only after their best years are over.

Hopefully, neither the protagonist nor the reader will figure out what is going on until the end; although both will pick up enough clues to suspect the three women are somehow related.

The moral of the story: somewhere out in the multiverse is the perfect match for you, but you'll probably blow it even if you stumble into it.