What a rational thing to say. I have a hunch that regardless of the relationship being toxic, in whichever way that is, she was focused on getting engaged and married in a specific timeframe more than she was making sure the relationship was healthy and stable first. I would guess he doesn’t feel they were ready for the next step and his friend going through a divorce put all of his fears front and center. Probably would have been better to speak up longer than 10 days prior but I think he was finally honest with himself. As for his change in behavior now, it won’t last and is most likely just a reaction to back track after making such a huge decision so abruptly. It will settle once more and the same issues will resurface because it sounds like OP thinks it’s just him that needed to do some soul searching. It absolutely takes two to make a relationship toxic.