Stupid? He's probably the best Strain pilot, from what we can tell a decent tactician, can control a capital ship alone... If he's stupid, then the standards for smart people would be pretty high indeed.
I think what happened with him was a mix of his own surprise, guilt and above all a hefty dose of telepathy by Emily. Anybody can tell he's not really a mentally stable person right now, and wasn't ever after his encounter with Emily. But yes, he probably has quite a weak will.
I think his character is far better than most crazed villains out there.