My villain's motivation

Partly copied from another thread but this time i'm asking if this is a suitable motive for my main villain.

My story has a character named Sky. His motive is an unquenchable thirst for revenge. He was once a soldier alongside one of the main characters, an accident happens and he's left horifically scarred, as in shattered vertabrae, a compressed back, and destroyed legs. He's rebuilt using bone donated by said main character (he's got a healing factor so he's fine), but finds himself both incredibly short and in horrible agony due to his wounds. Doctors say he'll have the pain forever. An event happens that's explored in another arc, and suddenly the Main character stops coming to his bedside, the doctor's don't tell sky that the bone was donated, he's discharged from the army and his wife leaves him. The despair, coupled with his agony leads him to snap. He blames the initial accident that causes everything on the main character and vows revenge, to do this he'll do ANYTHING. Sky is supposed to be a meloncholic who hides his depression under smugness and anger. The only thing that's keeping him on his feet most of the time is a single minded quest for revenge. because of this, he barely comprehends the horrific things that he does (even when he explains them). He can be reasoned with, but only by the people he cares about (which in this case are his 2 dragons), and they agree that his quest for revenge is warranted. Is this a believable motivation?

I'd say so. It does seem to be a case of Poor Communication Kills though, since if the Hero had just told him about the donations, he probably wouldn't have felt so abandoned. Of course I could have missed something in the paragraph, so correct me if that is so.

Well after the donations, the hero stumbled across something he shouldn't have seen (the origin of one of his team mates actually). His bosses couldn't risk him knowing, but they also couldn't afford to lose his battle skills. So they tried to wipe his memory. It ended up working too well and his mind was all but turned to mush. In his delirious and temporarily mindless state, the hero fled. Knowing that he no longer knew anything, the military let him go, but they also hushed up anything related to him, like Sky's surgery.

Seems like a decent motivation. I always somewhat dislike those sorts of stories, because it seems a little bit tragic to have the entire horrible conflict of the story grow from a single misunderstanding, but if tragic is what you're going for it works.

Ah, okay then. Now it seems less like Poor Communication Kills and more like pure bad luck on both characters parts. The main character got mind wiped because he saw something he shouldn't have and thus couldn't continue helping Sky, and Sky was unable to know this, thought his friend abandoned him, and thus sought revenge due to the delirium caused by the pain and the knowledge that he'd live with it for the rest of his life. I'd say it's believable.

I don't see him turning evil just from the accident, myself. Plenty of people have chronic pain that can be blamed on the actions of another person, and they don't turn evil. A more realistic reaction would be depression, and then eventually deciding to live his life despite the pain.