Theme of letting someone go
I haven't seen a lot of commentary on the theme of letting go, I see mostly the essential concepts established by Clark and his self-destructive behaviors and Mary processing her own trauma as a child, but above that I got the story of have to let people go. Mary has a hard time letting anything go.
I could have gotten this theme because of where I am in my personal life right now. I'm going to do a second watch today.
I connected a lot with Mary's character once she wound up in the backrooms. Absolutely terrifying from her point of view:
Starting with Clark choking her out, I started thinking about how that's one of my worst fears- somebody I thought I knew and could trust... killing me?
But he didn't kill her, she woke up bound and as Clark went on the more it seemed like he was going to kill her. She was terrified, and felt betrayed: she got too close to this person and now this is how her life ends. I imagine as a psychologist that fear appears every once in a while, especially with the emotional angry outbursts like Clark had earlier about 5150 and making her owe him an apology...
Then they go through the regression together, her being forced to support him when she's loudly in need of freedom. Previously, she had done it voluntarily, it was her job to... but now she has no choice but to do it, she's bound and feels threatened. The forced nature of the emotional labor made her lose her controlled cool in gently trying to help Clark look in the mirror of himself and she engaged with him as the broken person she actually is, instead of the composed person she pretends to be to help others.
In dropping her cover of a composed person, she realized that she can't save him, it's not in her control. She can't save anybody. She started thinking about what made her want to save people- and what made her think she could. Like Clark, she was running from her own history and avoiding the mirror of herself. Looking at anybody else's was easier.
When the monster (Captain Clark) ate Clark: Clark was literally embracing it, "she said we don't have to change". I interpreted this as Clark surrendering to the darkest parts of himself, not only unable to be saved but unable to save himself. The worst case fear of what could happen when you cant hold someone up anymore and let someone go.
From there, in the chase sequence, the monster not only looked like Clark- it had Clark's sadness. When it was on top of her, he looked so desperate and sorrowful I almost felt a sense of empathy for it. She had to stop him from holding her back though, it never ends well, she had to let him go. She wasn't able to get away until she embraced her own history, via the concrete, which ultimately is what saved her.
Clark's life was a mess of his own making. There's implication that he was at least emotional cruel to his ex-wife, maybe worse, but for a moment it felt like she was realizing he was an absolute madman, a murderer- but he wasn't, he's just a mess of a man and drags everyone down with him and keeps them there, his ex wife, Kat, Bobby. She was no different he would drag her down and keep her there because he doesn't want to live any other way... the only way to help herself was to let him go.