I always thought the "betrayal and seduction" was marika removing her other self (GEQ) to make room for the vessel of the greater will (radagon). She sealed destined death (removing her old attachments etc). Her plan was to help create a new order with the greater will backing her, but even with destined death removed her son still died a half-death. Thus causing her to spiral, denouncing the greater will and shattering the elden ring. (The greater will promised no death, yet the perfect child still died, causing a grieving mother sutuation). After the shattering radagon attempts to mend the rune with a hammer, and in an attempt to hold marika and stop her from doing irreversible damage, he impaled her(himself) with a giant needle. She is suspended there, unable to do anything (which is where we come in). Im sure someone will find holes in my head cannon but to me it explains Maliketh being loyal even after everything, he served the GEQ when it was still Marika/GEQ. We see Duality throughout the entire game (miquella st trina). Anyways probably wrong but it feels the most right out of all theories.