What I got from it is that he used Alexa to regain the lack of control he had in his relationship. Whenever he was with Heidi he knew he didn’t wanna be with her but didn’t want to say it.

He knew he was complacent with his relationship status wise, but he was completely unsatisfied with it functionally. He was still in the mindset that he had last season. “I must say this in order to maintain having a girlfriend. There’s a script I must follow. That script is fail safe.”

This episode was him FINALLY breaking out of that submissive mindset by reminding himself that having control over something, anything, is what made him feel less stress. Because he had absolutely no comprehension of how to handle the relationship he was in. He had so little control that he was panicked, and stressed, and he rooted it to her. 

That’s why he called her abusive – because whenever he was around her, he was stressed. He in his little child brain figured that it HAD to be her, because he doesn’t get complex emotions like that.

Because for two whole seasons he was brainwashed into being PC, he had to think about it in a PC term. He had to think of a way to break up with her without disagreeing with her and make himself the victim. That’s the way he could justify it in his brain.

But at the same time I think this is Cartman’s reawakening, by reminding himself that he doesn’t like being submissive, that he likes being dominant in some form, he’s finally able to free himself from the stressful guilt trip that became his relationship. 

This episode signals Cartman’s true return, IMO.