The 90% stat is in the original paper. Duh! The linked articles are summaries/abstracts.

"The paper, "Who Wants the Breakup? Gender and Breakup in Heterosexual Couples," was presented on Aug. 22 in Chicago at the American Sociological Association's 110th Annual Meeting.

To obtain a copy of the paper; for assistance reaching the study's author(s); or for more information on other ASA presentations, members of the media can contact Daniel Fowler, ASA Media Relations Manager, at (202) 527-7885 or pubinfo@asanet.org."