B: Dude, she only has the cats because she knows you hate it and is trying to drive you out. I guess you can't see the forest for the trees.
When you are too close to a situation you need to step back and get a little perspective. When you do you will notice there was a whole forest you couldn't see before because you were too close, and focusing on the trees.
Simply that you have focused on the many details and have failed to see the overall view, impression or key point.
He is so caught up in her affectation that he " cant see the forest for the trees"
He is to busy on the outside looking in that he cant see the forest for the trees.