I've been thinking a lot about Essek's "I've not cared for anyone but myself for the century I've been alive" line in c2e97 in light of the new Deirta Thelyss lore and Matt's revelation that this was going on during the campaign as well.
Actually, this line is what made me skeptical when we first saw Essek with Deirta in the animated show. There's Essek, seemingly deeply caring for someone- so how does that align with what Essek says later? My first instinct was to distrust what we saw with him and Deirta, to wonder if he actually disliked his mom and this was just another moment of Essek manipulating someone. But after going back and rewatching the e97 scene as well as the animated show, I can see how these moments can work together. And given the intentional imagery of Essek releasing his cantrip and standing in front of his mother rather than floating as he does everywhere else, the show is certainly indicating that in this moment, Essek has taken off all his masks. He loves his mother.
In e97, Essek is the lowest he's ever been. He may not be seeing things entirely rationally when it comes to his life and his relationships. He's clearly already been in the self-loathing stage for a while as he's realized he's come to care for the very people he's been manipulating. Essek has been examining his life choices already. It wouldn't be too much of a stretch to assume that he is also re-examining his relationships with Deirta and Verin.
By this point in the campaign, Essek may have realized just how selfish he's been in regard to his mother. He isn't ready to lose her, and he is prioritizing that selfish interest over what is best for her and her actual wishes. We as viewers can see that there is real love there as well. But to his mind in e97, what he has shown toward Deirta isn't real care for someone else. It's just another example of his selfishness. And even though we know Essek does care for Verin, he may also see his actions toward his brother as selfish. There's already been fandom speculation that he has not shared the extent of Deirta's condition with his brother, perhaps because Verin would disagree with his decisions. Perhaps he's intentionally keeping Verin in the dark about how bad things have gotten with their mother.
So I do think that, in his mind, Essek is telling the truth to the Nein: he has only ever cared about himself. However, with time, he may see things a little more rationally and recognize that real love for his mother and brother was there alongside the selfishness.