Was this in the reddit chat? I actually had to turn mine off because I kept getting messages from random people like this, mostly people looking for answers because they were going through similar stuff but there was a few that were just, idk, weird or lonely.

One of the messages wasn't quite as creepy as yours but it was similar. they would mention something from my comment history in this sub, they tried to relate, say something bad about the ex, try to compliment me then suggest we talk elsewhere sometime.

It's possible it is your ex but I think it's more plausible that it's just some random lonely, desperate person, scammer or a predator. Creepy either way.