She Moved On Quickly
Some people just can’t not be in a relationship, so they hop from one person to the next, rarely ever being single. That means, they never truly get a chance to figure out themselves or what they want. The OP’s friend was about to get married to someone exactly like this.
They would constantly fight because she was insecure and would keep accusing him of looking at other women. It seems like she eventually couldn’t handle her insecurity so she ended up canceling the wedding just days before it was supposed to happen. You’d think she’d take time to recover from that but apparently, she was with someone new within weeks. He had a close shave for sure!