The entirety of Final Space hinged on the relationship between Gary Goodspeed and Quinn Ergon. Their first meeting on Earth set in motion a series of events that were predestined and could not be undone. Simply put, they were meant to find each other. But a Season 3 episode showed that their relationship was one-sided in the worst way possible, and as difficult as it was to reconcile, they continued to work together.
At the end of Season 1, Earth was sucked into Final Space. At the end of Season 2, the gang fought their way into Final Space after it to save the world, free Bolo, and save Quinn. Ultimately, they were successful in freeing Bolo and saving Quinn. Unfortunately, Earth was turned into a pile of space rubble by the Lord Commander becoming a Titan in Season 3. The only upside was that HUE finally got to see Paris first.
One thing that the crew discovered in Final Space that they weren't expecting was a seemingly endless supply of dead Garys. They were inhabited by Invictus, who used them as his own personal army. Each one of these Garys ended up there after sacrificing themselves to prevent Invictus and his Titans from crossing over into their reality. It turns out that any Gary in any universe is always a hero.
But in the reality shown in the series, something different happened. Nightfall, a future version of Quinn, realized that the strategy needed to change. Their normal plan to stop Invictus failed in every reality. This time, Quinn was the one who sacrificed herself to prevent the incursion from happening. This left Gary and everyone else on the other side, trying to figure out how to save her.
Season 3, Episode 11 upended things a bit. The crew was able to free a dead Gary from the control of Invictus and ask what happened to him. That's when he explained how all the Garys came to be there, relating the story of all the sacrifices they had made. What he said next was more surprising. This Gary revealed that in every other reality, their Quinns never came to rescue them the way this Gary rescued his Quinn.
There was no time for Gary and Quinn to unpack the implications of this revelation. The idea that Quinn never tried to save him in any reality would have weighed heavily on both of them. Despite not really ever getting to explore anything close to a normal relationship, they had a strong bond formed by facing impossible odds. But this revelation seemed to indicate that the bond was stronger in one direction than the other.
At the same time, it's also worth noting that this version of Quinn sacrificed herself so that Gary didn't have to. How this version of Gary and Quinn differed from all other realities never got the chance to be fully explored before the series was canceled. But it's clear this iteration of this dynamic and heroic couple had the best chance of stopping Invictus, because they were willing to make choices that no other versions of Gary and Quinn were willing to.