Meeting the Ex, Too
As bad as meeting your date’s mom on the first date is, it’s nowhere near as terrible as meeting their ex-boyfriend or -girlfriend. The OP had been dating for about a year when they decided it was time to meet his parents. Somehow, his ex found out about the meeting and invited herself over.
Why anyone opened the door for her, we’ll never know. But what happened was the ex came and talked about all of the lovely experiences she had with the OP’s BF. It was clear that she was in a bad place mentally, so it didn’t ruin the OP’s relationship with her BF. In fact, the two wound up marrying each other!