I wrote this for another thread in this subreddit a while ago, but I might as well share it again.

Here's my prediction for the next two seasons. I know it looks hard and daunting to read all of this, but please give it a go.

What if in season 7 Debra uses her role at Lieutenant to help Dexter, slowly becoming a political shark like Laguerta. In the meantime, Quinn starts giving a fuck about his job and while he's trying to become a better person he finds out about Dexter and how Deb is using her power to stay out of trouble. Because he is spiteful towards Deb for dumping him, and he never got along well with Dexter, he tries to destroy both of them and become a hero. Deb then finds out that Quinn will tell Laguerta about Dexter's killing sprees and Deb's support, but wants to milk the situation. Anyways, Laguerta ends up dying because Quinn fucks up somehow. In order to try and tighten up all loose ends, Deb manipulates Dexter into killing Quinn, since she is on a power trip caused by her more aggressive personality at work. Plus, now that Laguerta is gone she is unopposed.

When Deb convinces Dexter into killing Quinn, this is in direct violation of Dexter's code, because he didn't actually do anything wrong. Quinn is just a giant douche. Debra is completely fucking with Dexter's moral compass because she just doesn't "get it" and uses the biggest rule of Harry's code, which is "don't get caught!" to justify her actions. The season ends with Deb having to kill someone in cold blood for the first time, and she kind of fucks up so Dexter has to clean up her mess. Dexter goes apeshit and goes on an epic dialogue about how his burden and how he never got a chance at a normal life. Dexter finally really connects with Debra, and they share a moment. Debra is no longer in love with Dexter, but she realizes that she is in love with what he represents. End of season 7.

Season 8: After they have that emotional heart to heart, Debra realizes that Dexter has always been there when she was in need, so she wants to be there for him too. She convinces Dexter to become a doctor and realize his full potential, instead of just working in a crime lab. She thinks she can change him, and give him hope that he can truly rid himself of the dark passenger.

Dexter has to learn to adjust to working in a hospital, and he may eat his lunch in the morgue from time to time until he realizes that it is not acceptable. He eventually learns that helping people can be very rewarding, and sees that people who have had their lives fucked up can turn their themselves around. With Debra helping him along the way, Dexter realizes that there is hope after all, and Harry was wrong to assume that his son would never live a proper life and learn to get rid of his dark passenger.

So at the end of the show Dexter finally realizes his full potential and goes on to live a happy life with his son. In the meantime, Debra sees that Dexter can change his life around, and even though she had some extremely terrible experiences in her past, the future isn't so bleak after all.