"Maybe one day you'll call me, and tell me that you are sorry, too."
That's what both Spencer and you have been thinking the whole time, after your relationship abruptly ended. It has been four years now. You were there during the whole Tobias Hankel case, meaning that you were here during Spencer's addiction since you were his partner and also his collegue at the BAU.
He blamed you because one small mistake led to the wrong geographical profile, and that's why the team was late. That's why the team didn't get here in time to save Spencer from Tobias. He knew it was irrational, you didn't mean to get the profile wrong, but my god, he blamed you so much. Your guilt was eating you alive.
But then, during your last fight, he said something too hurtful. You confronted him about his addiction and the fact that he needed to seek some help. You desperately tried to give him an ultimatum, too. It was either you or the dilaudid. And that's when he said:
"I'd choose literally everything over you. At least Dilaudid makes me feel something, it makes me feel something."
And that's when your relationship ended. This was the last thing he ever said to you, and also the last time you saw each other, since you alto got resigned to another unit in a nearby city.
Unspoken words and unresolved conflicts bought the two of you to look for ta glimpse of the other in other people, trying to move on and to fill that void that the other one left.
Now, after four years, you got invited to JJ's babyshower: she was going to have another baby and you had to be there. She invited your boyfriend, too.
But well, the situation becomes slighty embarassing the moment you bring along your boyfriend, who is basically a Spencer look-alike, and Spencer brings over his girlfriend... guess what? Your copycat.
You aren't talking to each other, but you could feel his gaze on you.