Why can't Rhaenyra let go of Alicent, despite everything she's done to her?
I won't talk about the symbolism and the nostalgia, it's an answer. But there's another one:
It's Rhaenyra acting like Rhaenyra.
This lasting love is the raw manifestion of her personality. She's ambitious and spoiled. She's been a princess of a colonialist family, the heir, the favored child. She's used to things going her way, she can't stand when they don't. She's always gotten what she wanted.
Daemon? Criston? Harwin? Mysaria? She got them.
Feeling as valuable as a son in Viserys' eyes? He named her heir and deeply neglected the sons he pushed Aemma to death for and raped out of Alicent.
New dragons riders? They came to her.
Chosing who she married, when and who she had children with? That as well!
But Alicent? Rhaenyra's wanted Alicent long before the throne. Maybe even before Daemon.
Alicent was taken away from her. Alicent was rubbed under her nose for two decades. Married to someone else. Raising kids that weren't hers, βin her eyesβ loving them more than she loved Rhaenyra. So close, yet so far.
Alicent is her deepest, oldest desire. Alicent is the one thing Rhaenyra never got. This familiar land she still hasn't conquered. It frustrates her to no end. She is her greatest obsession.
Rhaenyra can't get over her because that's the way she is. She wants to possess Alicent. It doesn't matter how much Alicent hurts her, how many times she betrays her, in how many ways she escapes her, how much resentment builds between them. That frustration lingers because it's a whim.
Rhaenyra needs to get the things that she wants, one way or another, soon or late. If what she wants isn't avaible, she goes for something that can replace it, however without giving up on her first desire. That's what she's always done.
Alicent isnβt any different. As long as Rhaenyra hasn't acquiered what she wants from Alicent, as long as she won't feel like Alicent is hers, that Alicent has chosen her, as her jealousy isn't appeased, that feeling is going to last.
There's genuine love but the persistence is ego driven.
Once you've accepted how much of a selfish and stubborn person Rhaenyra has always been and noticed her vicious patterns, her undying love for Alicent makes plenty of sense.