One of the things I absolutely love about Agatha and Rio's relationship is the nuance that Kathryn and Aubrey are bringing to how they play their interactions...
Rio always looking at Agatha with regret and sadness and longing, knowing that even though she had no choice, that she had a job to do, that job lost her the woman she loves - this is why Rio sees Agatha as a scar, as a reminder of who she is and the things she had to do that she didn't want to do.
Agatha *knowing* in her soul that Rio was just doing a job, *knowing* that she's not actually mad at Rio, but that she just has so much anger and no where to put it - this is why the second Agatha is put into a vulnerable position (i.e. almost losing Teen), she immediately falls back into Rio's arms, because Rio has always been her comfort, has always been her person, and when she really needed it, all of that anger fell away.
Honestly? There's a part of me that thinks Agatha is going on this journey down the witches road in an attempt to get her powers back so that she can get her son back (if that's possible - we still don't really know what happened) and Rio knows this, which is why she reminded Agatha that Teen wasn't her son, because she knows Agatha, and she knows that what's driving Agatha is that anger, so even if it means Rio loses that closeness again, she's going to do it so that Agatha can get what she needs, what she deserves
