He's selfish af and this is the worst. Being deluded is a close #2. I've watched this series so many times and this is the only time I can remember being genuinely mad at Dexter's actions and attitude. He does sooooo much mental gymnastics to convince himself his actions are for the betterment of all involved. Just admit it's strictly for you and your enjoyment. At least admit it to yourself.
He spent every season since Rita died regretting that he didn't kill Trinity immediately versus just regretting that he ditched his family (cover? cuz imo he mostly treated them like cover deb not incl) several times to hunt/stalk/have dates with Trinity and his family. Which is what actually got Rita killed. His selfishness.
Watching s7 again and he genuinely is trying to break Deb and rebuild to fit his wants (being fully accepted by someone he loves) and he believes he's doing it for her/them. It's strictly for him. Doesn't even care to see that he's actually splitting her in half. I'm a fan of Dexter but he's also focused only on himself, using his family as accessories and doing just enough to convince everyone to stay and fulfill their roles in his life while he does what benefits himself only. Then gets frustrated and mad they need him to fulfill his role because it's inconvenient.
I guess he's better-ish now that Harrison is an adult but? Not really.
TLDR: Being a serial killer is okay but consistently using and mistreating the people who love you is where I draw the line. Schedule your kill process around your family/friends not the other way around!