He's right, you needed more affection points with her at that point and there was only a small margin for error. Either accept the loss or go back and try to make things right. You should probably go through the offical walkthrough and check all of Rebecca's decisions to determine how far you need to go back. The official walkthrough is among the game downlads.
I had a similar dilemma and decided to make a guidance mod some time ago, to end the fomo once and for all.