Disclaimer: I don't own Criminal Minds and never will. No copyright infringement intended.
Erin Strauss and Alex Blake have both silently agreed to not discuss other parts of their history together. No one will ever find out that they were once a couple, something that was true even during their relationship.
Erin deeply regrets not speaking up when she had the chance, but it was just one of mistake of many that led to the end. She was just terrified that someone – like their boss – would find out and her career would be ruined. Work was – and still is – important, and she didn't want to lose it. But she had ended up losing Alex in the process, one of her many regrets. Fear ruled them back then. They dated out of town and made love in the dark so no one would ever know. But she can't bring any of this up to Alex now, especially as she is her superior. Besides, it's in the past. No sense in talking about what could have been.
She does think about the happier times occasionally, more so now that Alex is part of the team. What would life have been like now if they had just come out? If Erin had defended her when she had the chance? Would they still be together? Happy? But she tries not to think because the "what if's" drive her crazy and there's no sense in that. Erin's worried it might send her right back to the bottle if she doesn't move on, and she has to. It's been a long time and she's had many relationships – Serious (and sometimes just sexual) since then.
Erin Strauss is just going to have to deal with what her life is like now and do her best to be friends with Alex, if she lets her. It's all she asks.
Alex is happy now and she doesn't have any regrets. Well, maybe. She's probably lying to herself again. She's confident in her abilities and she likes her new team, despite getting off to a bad start with Garcia. She loves catching the UNSUBS. It's pretty fulfilling. But she's bothered by Erin's presence. She won't let her know that, however. Erin's her boss and she refuses to let their past be a problem. She can't help if it she sometimes gets flashes of amazing kisses in the confines of their bedroom and what happened afterwards. But those are few and far between now. It's been years and she's happy with her life and husband now.
Alex will never regret her relationship with Erin, but she'll never say that to her. Erin deserves to suffer just a little bit for what she put her through, especially after she didn't stick up for her on that case. She'll try to forgive her – Up until she started working for her, she thought she had – and do her best to be civil. She'll be professional and won't let this get in the way of her job. She just wishes she could ask Erin "why?" She'll be satisfied with whatever answer is given.
When Erin and Alex pass by each other, Erin stops and that's when she decides to stay something. However, her mouth opens and closes a few times before she can get a word out. "I…" She trails off and is unsure of what to say. What can she say? Her actions were unforgivable, and she can't change what she did. Besides, they're at work and she is Alex's superior now. She just has to keep reminding herself of that. It doesn't matter that she's still sometimes in love with her ex-girlfriend. Nothing's going to happen.
"What? Is there something wrong?" Alex knows what her boss and ex-girlfriend is doing, and she's going to shut it down immediately.
"Oh, nothing. Never mind. I completely forgot what I wanted to say. Enjoy your day!" Erin turns to walk around, but is stopped dead in her tracks.
"I will. My husband and I are going to go out to dinner and enjoy ourselves tonight. We're really quite happy together." Alex immediately regrets her actions as soon as the words are out of her mouth and she feels bad when Erin's face falls, but she isn't going to apologize. Erin needs to know where she stands.
"Of course. Enjoy yourselves!" Erin smiles and then bolts back towards her office to think about her idiotic actions. Nothing is ever going to happen between them and she needs to get it through her head. That ship has sailed and it will never come into the harbor again. It's time she finally accepts that.
It will be torture for Alex and Erin to have to work together and be in the same building most of the time. They will always have unfinished business.