Did Sebastian ruin Tyson's life?

There is certainly a strong argument for this being the case, one Tyson had made many times; in some cases to Sebastian’s face. However, it’s not something Tyson really believes. The only times he’s stated it is when very angry or upset.

If it wasn’t for Sebastian - The Colonel - Tyson would have never have proven himself. One of Tyson's strongest attributes is his will to survive; his instincts for survival are (almost) as strong as [Sebastian's] instincts to kill [are]. If Sebastian hadn't put him through everything that he did, would this have been revealed?

Unlikely. Tyson plays everything safe: he plays, he played, and he will play it safe. He isn't a man to freely take risks and, aside from joining the army, the biggest risk he's ever taken was getting close to the sniper.

Tyson's not doing to admit it, but Sebastian made him; into practically everything he is today. If it wasn't for Sebastian Tyson wouldn't be where he is today. He'd never have proven that he doesn't need anyone to save him. He would have never gotten himself to a point where he was interesting enough to take Moriarty's interest.

Without Sebastian, Tyson would have served his term in Afghanistan then retired to teach mathematics at Cambridge, just like his father intended him to. Tyson would have considered his life a failure, he'd have ended up where he started with nothing to show for it.

Sebastian certainly ruined Tyson's body: the dent in his torso isn't a repairable injury, if it was Tyson would have repaired it a long time ago. The trauma of the events he went through with, and at the hands of, Sebastian certainly increased Tyson's fear and social anxiety, but they weren't the cause for most.

It would be easy to say that Sebastian ruined Tyson's life. He certainly obliterated the life Tyson had, but the life Tyson has now is better that it would have been without The Colonel's influence.

It's not just that Sebastian forced Tyson to prove how strong he was. If it weren't for surviving those events, Tyson wouldn't have the confidence in himself to show how smart and talented (mathematically, cartographically, and with dogs) he was either.

Tyson is hard pressed to admit it, but Sebastian is important to him. Try as he might, Tyson cannot hate Moran nor can he want him dead, not really. Tyson cares about him too much. He will always come when Sebastian calls. Tyson isn't grateful for what Sebastian did to him, but deep down he knows that - ultimately - it changed his life for the better.