There was also the DS9 episode "Rejoined" that aired October 30, 1995 (so it's close)
But this is actually a really interesting question as to whether it qualifies as a same-sex relationship. The episode's about Jadzia Dax encountering a former mate. For those who aren't familiar with DS9, Jadzia Dax is a Trill and as such is actually a symbiotic pair of two organisms - the Trill symbiant and the Trill host. It's a little like the arrangement in Stargate: SG1 except obviously the Trill aren't intergalactic totalitarian power hungry despots. The Trill symbiants tend to live much longer than their hosts - barring a disease or disaster that would kill the symbiant through trauma, they tend to survive through about 10 hosts. But statistically, so many joined Trill end up in situations where the symbiant can't be saved that not all that many make it past 6 or 7 hosts - so the ones that do are considered to have really "been around the block". Jadzia is just such a host.
But the crux here is that Dax encounters a former mate - Lenara - who she was married to when she "was a man" (her host, Torias, was a man), and Lenara was "Tolani" (a woman). Torias died in a shuttle accident and Tolani went on as a widow. Tolani eventually died and the symbiant moved on to Lenara, but all of the memories and emotions are shared. It's one of the central aspects of this episode that the organization in the Trill government that dictates the policies of joined Trills specifically forbids / frowns upon Trills interacting with former mates or people they knew in their former life. It's a very imperfect policy, what with hundreds or thousands of joined Trills running around, it could prove difficult to avoid encountering former husbands, wives or even children.
But Jadzia and Lenara strike up their old flame for awhile. So this might count as a same-sex relationship.