Voltron Spoilers

It essentially starts with Kuron and his subconscious mission to infiltrate and destabilize Voltron. So he takes a liking to Lance (who has an unrequited crush on Shiro) and that's when his subconscious kicks in and starts tearing him down mentally by insulting and gaslighting Lance. But because Lance actually starts improving as a pilot and fighter out of sadness this isn't what Kuron was supposed to do. So after some time they find Matt and Shiro and try saving them and that's when Kuron (whose objective is found out about now) takes his chance to bring Lance with him to the Galra where he is interrogated but since he's already essentially broken, he doesn't even put up much of a fight and believes he deserved this. He loses one of his eyes and his entire left face, upper body and arm are burn scarred from an interrogation. Meanwhile Kuron is suffering a meltdown because he just betrayed the guy he had a crush on.
After Lance had been tortured he is brought to the gladiator ring where he soon gets a reputation as a "second Champion" because as a paladin he obviously is much harder to fight even if he doubts himself and sometimes barely survives because his specialty isn't hand to hand combat but shooting.
Kuron knows of all of this and is the one who eventually helps Lance escape after he had been in there for one and a half years by providing cover and distracting everyone and Kuron is lucky that nobody (seemingly) finds out about his schemes. When Lance escapes he gets to the nearest planet which is by then under fire by the Galra (just in time, ayy) and he as the former blue paladin offers his help to the people. With his help they are able to fend the intruders off and Lance offers them an alliance to help save other planets.
Now, cue to one planet where he is forced into marriage with the daughter of the oppressive ruler of said planet. This alliance is especially important to him because the planet is rich in materials the other planets in his alliance need. Because reputation is very important on that planet, he has to claim to still be the blue paladin and of course they want proof of that and see the other members of Voltron. That's when he gets into contact with the team again and tells them about his problem. The team meets him again after 2 and a half years and are overjoyed yet saddened to see how their friend, who put so much importance into looks looks like now: Apart from his scars, both of his lower legs are prosthetics because the real deal was crushed under a rock and he is not only half-blind but half-deaf. Lance has to stay calm, even though he is just as happy to see his old teammates (he doesn't use the word friends anymore since he is scared they don't consider him that anymore) to not let anything slip. When the rulers of said planet find out he isn't actually the blue paladin anymore (because Matt had taken on that role) because someone let it slip he is sentenced to public punishment while his friends have to watch.
When he is released the Galra attack and he helps Voltron fending them off, while still injured from his punishment, but Shiro and Matt with the Blue Lion are abducted set for an execution that would be transmitted all over the empire should Voltron not give in to their demands.
Luckily Lance sneeks onto the ship and is able to free them with the help of Kuron (because his love and guilt for what he had done to Lance is too crushing) and they all escape with the help of the Blue Lion. To be brought back to the castle where he is welcomed by everyone again.
When Allura (and maybe Kolivan, too, idk) however sees that he brought Kuron with him she starts attacking him and screaming at him for what he had thought to bring an enemy into their ship again. That he is too sentimental and that he hasn't learned anything. That's when the transmission by Haggar of his tortures and fights in the gladiator ring starts, accompanied by memories of being being bullied in school and screamed at by his relatives for being worthless and undeserving. Lastly it shows memories of Matt from when he spoke to the others and how they would compare him to Lance in a way because he fills that role now and how they talked about Lance deserving to be with the Galra for being too annoying and never taking anything seriously.
Lance tells Allura that he brought Kuron for him possibly having vital information on the Galra (apart from not being cruel because Kuron would be killed for what he did) but Lance agrees that he is a disappointment and that he should be less sentimental. He collapses then and there because he still has his wounds from his punishment and everything was too overwhelming for him.
When he wakes up two days later to Kuron from the healing pod they tell him that they spoke to the ruler of that planet again and that the alliance has been successful. Also, they found a way to break Kuron's connection to the Galra.
Lance thanks them and tells them that he will leave now to keep on doing what he did before. The others want to stop him and want him back with their team, that they want to make right what they did wrong and Matt tells him how much Blue missed him but Lance only says that Allura is right and that sentimentality doesn't win wars. He proclaims that it was his choice to do this and even if he missed his old teammates, he wouldn't do them any good. Besides he couldn't feel Blue's bond anymore anyway. Maybe they could meet each other on earth again once this was over.
Lance leaves with Kuron, who wants to make up for what he did to him. Lance holds no anger for Kuron but gladly takes his help.