I'm sorry but this whole character arc has been thrown into the trash and you all need to stop trying to analyse it and make it look reasonable. At the end of book 5 he gets a letter from Cersei asking him to help her and he literally throws it into a fireplace. Also, in the books he found out from Tyrion that Cersei fucked other men and never told him - he's really hurt in that scene and it makes him hate Tyrion because he doesn't want to believe it.
If you don't want to take books into account, fine, let's take a look at the show.
How could he still love her? What does this story tells us? That you can never escape a toxic relationship? That once someone manipulates and uses you, you're a lost case forever? That you can't redeem yourself no matter how hard you try? How is this a believable, well writen story? Why did we get so many seasons of build up and complex character arc hinting that Jaime was becoming a better man if all of this was useless in the end?
No one said he should've died at the age of 90 with Brienne by his side. What SHOULD've happened was a chance for him to finally redeem himself for all horrible crimes he did for Cersei and prove himself a good man he always was but couldn't be because of her. Their death doesn't make any sense.