they used to date. it was a longgggg ass time ago, before Sombra was imprisoned for the first time. Starswirl the Bearded had a school in Canterlot that Sombra travelled to attend. at the time, Discord was kind of sort of maybe acting as Starswirl's adopted son (it's a long story). but him and Sombra spent a lot of time together, and eventually fell into an on and off love-hate relationship (mostly love; Sombra is a total head-over-heels hopeless romantic, and Discord loved that).
Discord saw his corruption coming from a mile away. he's really, really fucking old; he watched from the sidelines as the Umbrum were forcefully removed from their home, with thousands being slaughtered in the process as Celestia worked day and night to cover it up. she did a damn good job. no one in Equestria was educated about the Umbrum or their existence in the Arctic North. Discord saw Sombra's Umbrum blood, and considered on occasion telling him about his heritage. but he didn't want to lose their relationship. in the end, the consequence for ignoring Sombra's familial relations ended up being what separated them.
as Sombra began his first, brutal regime, the lord of chaos sensed a small mental change in him. it was Alzheimer's Disease. Sombra had just stumbled over the edge of a long and tortuous downward decline in his mental health. Discord felt it in the deepest recesses of his brain. he thought, quite foolishly, that interacting with him and keeping him intact with the outside world would keep him stable. of course, he was wrong, and Sombra slowly began to succumb to the illness eating away at his mind. Discord was distraught. he wished, more than anything, that he could save his lover from this awful grave he had dug for himself. but by the time he had realized how far gone Sombra truly was, the two sisters came to liberate the Crystal Empire. they weren't as receptive to his mental state as Discord was, and didn't see how imprisoning him in ice for five-thousand years would aid in his mental deterioration. Discord couldn't help anyway. he felt like a coward for running away from danger at the last second instead of defending Sombra like he should have. but there was nothing he could do.
he fell into a depression during Sombra's imprisonment, and it was this sudden snap from happiness to sadness that would cause him to slip into a rage and dunk the entirety of Equestria into chaos. that earned him an imprisonment, as well (though it was cut short as his magic built up and broke him free of his statue form as we see in the show). Twilight and her friends ended up turning him back to stone, and he completely missed Sombra's return (and consequential defeat). he was reformed by the time Sombra was found for a second time and began his own reformation, but he was nearly gone by the time Discord finally got to see him again. for the first few months of his reformation, Discord wouldn't visit him; he could sense his decline, and watching him decay like he was made him sick to his stomach. eventually, in the last few years of his life, Sombra received visits almost every day from Discord, until he was pretty much watching him alongside Sunburst.
it is thought that the day Sombra gained his wings was the day he was going to die. Discord was an easy indication of this. despite being married to Twilight at the time, and having kingly duties to attend to at home, he kept a constant watch on Sombra. he would later come to explain that he felt his magic would be able to change him or even save him. of course, this was just foolish naivety on his part. even Sunburst, who was pretty much living at the hospital where Sombra had been moved, was more relaxed than Discord; he sat by his bedside 24/7, and fought when security came to try and force him out of the room for some check-ups where he couldn't be present.
he was positively overjoyed when Sombra gained his wings. absolutely amazed. he saw a sudden, great improvement in Sombra's mental state and knew that he had been healed. unfortunately, the guy immediately fell into a 2-month-long coma following his ascension. Discord and Sunburst were with him every step of the way.
now that he's okay, Discord is, of course, a lot more lenient in keeping tabs on him. but he does still keep tabs.
considering how things went towards the end of their relationship, one could say that their relationship never truly ended. Discord and Sombra still love each other, though their relationship is more friendly and familial now than romantic. Discord does, however, still sometimes display affection towards him, and these displays are mutual to certain degrees. Sunburst and Twilight just kind of roll with it, and everyone else does, as well.
in summary: Discord still calls Sombra 'babe'
so yeah, just me, completely ignoring the canon timeline :)
i tried out CSP's design brush, and that was interesting. like the effect it gave. look at Sombra's sexy eye thoooo XD
Sombracord is best crackship. go ahead. try to convince me otherwise