Alternative Character Interpretation- Stella Keeps Tormenting Stolas With The Knowledge He Cheated Because She Knows How Much Of An Unapologetic Narcissist He Is
I think despite people saying she's dumb I do think she's socially more aware than people let on. I like to think she knows by now despite how Stolas presents himself as a nice guy he underneath is a narcissistic pos with a victim complex and no real empathy for others. She keeps tormenting him because she knows what he really is as a person and that calling him out on his actions will always get underneath his skin.
And he keeps proving her right over and over again. And if she wasn't a strawman hate sink the writers could have her talk back to him saying even if he doesn't think he didn't hurt her he certainly did hurt her daughter. And I would have her say it straight is that despite saying how much he loves his daughter he didn't give a shit his affair would cause her so much turmoil.