You could, in fact, say that the US government betrayed him. In fact, it did so twice. First, when it betrayed all of us, by acting against out interests as a populace and constitutionally mandated rights as citizens. Then, when Snowden saw the depth of the government's betrayal and tried to bring it to light, they betrayed him again (personally, but in a way with consequences for us all) by abandoning all those promises about whistleblowers and choosing to persecute and vilify him instead.
Personally, I doubt he actually has gone over to the Russians. Nationalism is a strong drive, and you don't get to work at the NSA and have a clearance unless you've got a good bit of it. On the other hand, somebody who was as strongly pro-US-government as you seem to be, but a little less blind and righteous about it, may have felt the depth of those betrayals deeper than I would. If it turns out he has gone over, I'm certainly not going to judge him for that. The USA has amply demonstrated it does not deserve his service or support, first in the actions of the NSA, then in the actions of the Obama government in general, and finally in the actions of the populace at large (who have continued apathetically doing nothing of consequence while the whole scandal unfolds, rather than stand up for somebody willing to take such a risk for the sake of freedom).