Knowing more about cage's tactics now that i'm maybe halfway through scavenger blood, i think i'm even more convinced that he was the one that convinced seamus to betray donnell, in much the same way he had hannah poisoning the relationship between donnell and blaze.
Given that donnell and all the division leaders were so hellbent on turning seamus into the next sean donnelly, to the point that they made him an officer at just 16, he was a much bigger threat to cage's plans of taking over the alliance than blaze was
Since seamus looks so much like his dad, cage couldn't use the affair child gambit like he did with blaze, so what did he do instead? My bet is that he convinced seamus that donnell had been having an affair with one of the new york women (possibly himeko?), and that was why he hadn't gone back to london or arranged to have keira, seamus, and blaze move to new york to be with him. And 16 year old seamus, who had just lost his beloved mother, and was somewhere new and scary and his dad was suddenly foisting all this responsibility to him - of course he'd take the nuclear way out. Of course he'd want to get as far away from donnell as he could, and deal a painful blow on his way out.
I do think that his anger clouded his judgment, and that was the only reason he left blaze behind. Maybe he fely betrayed that she was choosing their dad's side over his. And then once the new york portal relay network was already blown up and he was in beta sector - well, by that point it was too late for regrets, wasn't it? It was too late to go back for her.
I wonder what his life in beta sector is like? Had the discrimination against clanless people already been established by 2400? Did seamus take a gamble on finding a better life for himself, only to find himself in the exact same situation he had been in on earth, only this time he was completely on his own, without even his family by his side?
And then the new york firestorm happens, and he has a fresh new emotional wound to pile on top of the rest, a new nightmare to add to his trauma of the london firestorm, a new family member to grieve.
