retrosex
A hookup or other episode of sex (such as the start of a new involvement) between people who dated or hooked up way back when, lost contact with each other for years, and became reacquainted.
See: http://thephoenix.com/Boston/Life/75527-Are-you-a-retrosexual/
See: http://thephoenix.com/Boston/Life/75527-Are-you-a-retrosexual/
She's not dating anyone right now, but she's had retrosex with two guys she hasn't seen since high school who she found on Facebook recently.