: Well we don't know wether or not Deceiver would betray
: alric or not since he 'died' at shiver (I personally
: thought he would betray alric) but the reason he
: helped Alric against SB is because the other fallen
: lords all hated the Deceiver, so he couldn't join SB
: and Shiver, because shiver and SB would kill him. And
: he joined Alric because he owed alric his life: Alric
: helped him get the Staff back that gave him freedom.
There's also one theory that the Deciever helped Alric partly because he felt loyalty to the Empire of Cath Bruig, as suggested in Shiver's line which goes something like "Will you follow anyone who claims the crown of Cath Bruig?". The reason why he served Balor was because the Deciever knew Balor while he was still Connacht, and, as such, the Emperor of Cath Bruig, to whom he had sworn allegiance. True, Balor did level the Cath Bruig Empire, but, in theory at least, all those he killed were followers of the usurper Ceiscoran, so constituting treason, and justifying his actions.