Quoting Dagny: He said sometimes he feels like we are back and other days he doesn't. To be honest, I feel the same way, but obviously I am not going to throw the towel in over it.
In a round about way, its his way of saying that it is getting better. At one point, he felt the bad times outnumbered the good ones. Now you're somewhere in the middle, but its enough of a change for him to realize that it can continue to get better to the point where the good time will far outweigh the bad.
... but its a slow process, one that takes a lot of effort to stride for those good times. He did turn it around by asking what bothered you and apoligizing altho it did seem to take a turn for the worse before that. Now what can be done to turn it around before that? While you can't control his critizism, you can attempt to keep him from harping on it. Tell him you got the point and will try to do better next time. If he continues, remove yourself so that you both get a cool off period where calmer heads will prevail.
All it takes is one point in the dynamic to change the total outcome. Before reacting to what he did, take a moment to think what can I do to draw us closer right now? Its a matter of asking that first to find what works, rather than getting caught up in old patterns.
