Alright here we go for Thalia and Luke for the ship weeks!
I realized I had a lot of feelings about this couple because it’s impossible for me to think of them as happy and adorable. Because like they were best friends, they trusted each other more then anything. Luke was willing to follow her anywhere and Thalia was willing to die for him. Thalia didn’t really believe everyone when they first told her about what Luke had done. She didn’t believe that her best friend could become that until she saw it for herself. He did disappoint her in end and it broke her heart.
And as for Luke I think that if Thalia hadn’t died and been turned into a tree, she would have been able to keep him from working with Kronos. She would have been an anchor of sorts, or a voice of reason when Luke was at his lowest. I suppose her death broke something in Luke too. It wouldn't surprise me if her tree became a source of resentment after a while. Maybe he couldn’t even see the tree as her, and it was just some cheap replacement to him.
So I always imagined that they could have had a moment like this where Thalia looks at him and tries and tries and tries to find her Luke in this boy who has been burned out by hatred and bitterness and anger. She’d wait for him to smile or laugh because that’s what her Luke would do, but he doesn’t because he isn’t that person anymore. Her Luke is gone. And eventually he has to pull away from her because he already let her go a long time ago and he can’t go back. They really could have been so much more. Sorry for rambling just ugh