Is there a psychological term for finding your former partner sexually attractive, or for wanting to get back with your ex? How does science describe this condition?
FWIW, I've tried to find existing research on this and come up with next-to-nothing. Hypothetically speaking, I doubt it would be constructive to adopt new psychological jargon that even social and personality psychologists (like myself) have never heard of, given how little research there appears to be on this. The closest match I found was the following reference, which doesn't really discuss sexual attraction or infatuation:
Rubin, Z., Peplau, L. A., & Hill, C. T. (1981). Loving and leaving: Sex differences in romantic attachments. Sex Roles, 7(8), 821–835. Retrieved from http://www.peplaulab.ucla.edu/Peplau_Lab/Publications_files/Rubin_Peplau_Hill_81.pdf.
Anyway, if it's jargon you want, you might consider passion, lust (this has somewhat more negative connotation than I'd expect an author to desire, but at least one article uses it), limerence, or infatuated love. These don't connote the existence of a broken commitment, but infatuated love does connote a lack of commitment or intimacy by Sternberg's definition, and all connote sexual attraction.