After parting ways with my companions, I started sabotaging other players...
Literal
Companions [with-と] parted [from-てから], other players [object-を] interfering became...
仲間と決別する ('to part ways with companions, to break with one's group') uses 決別 ('decisive parting'). 他のプレイヤーを邪魔する ('to interfere with other players') uses プレイヤー (loan) and 邪魔する ('to obstruct'). ようになった ('came to do, started doing') marks the behavioral change. The trailing ellipsis and ・・ suggest regret or continuation. A gaming narrative about a player going rogue.