Great question — answering as the UphillTech team:
When Vader killed Padme in anger he lost his reason to live, he'd betrayed the Jedi order (using Palpatine's fictitious uprising as an excuse) and committed murder to increase his power and gain the Sith Lord's trust. No doubt up until this point he had ambitions of saving Padme, reforming the republic with them at it's head and giving her everything. A dark and twisted devotion to her. After her death he no longer had these motivations, I believe the fall to the dark side is very much about self deception and finding justification for your actions - after all everyone is the hero of their own story! He blamed Padme's death on the fact she'd betrayed him (bringing Obi Wan to kill him), the...
Full answer by Liath: https://movies.stackexchange.com/a/16477 (CC BY-SA 4.0).
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