Not really, he knew Horus failed and thought the previous Warmaster a complete fool. I really wish people would get the idea that Abaddon is a failure out of their head... He hasn't failed in any of the Black Crusades, they all achieved some specific purpose, they weren't all aimed at Terra. In fact, none of them have been so far.
Yes, the Black Crusades themselves were not failures as his objectives were met. I was talking about in the lore it's mentioned quite a few times that Abaddon has issue with only his beloved Primarch being the only "failed" traitor Primarch. Hence the rename to the Black Legion from the Sons of Horus.
That opinion only really changes when the body of Horus is stolen, sort of out of nowhere really. There isn't much of an explanation as to why he changes so drastically.
I believe he changes after going on the Dark Pilgrimage, stated in the Black Legion codex (Which I don't have at the momento). In the time that he leaves for that, the Legion praise Horus's body and so on, Emperor's Children come and nick it, then Abby comes back all ragey and stuff, then goes and kills all Fulgrim's warriors and destroys the bodies of their Primarch, renaming them Black Legion. I think he's gotten over the fact that Horus failed, he just has a huge hatred for the Imperium.
Well, it's possible that he's under the influence of the Dark Gods, considering when he was about to die by the hands of Eldrad on Cadia, they whisked him away before Eldrad could deliver the killing blow. EDIT: ah, nevermind I appear to be going on about something completely different..
Don't bring that up... It was from like 10 years ago and the Eldar players simply said that Eldrad killed him when he didn't.
