Sounds like you took all the kills, got geared, then did all of the damage. Causing you to take more kills. Thus your team got left behind.
Just because you have your R, doesn't mean you should always use it every time. If you know they're going to die, move to the next target.
Not saying don't get kills. But read the situation. People QQ about having 5x more kills than deaths in a game and say stuff about not being able to carry their team. When they lost because they didn't get their team fed as well and the game ended up being a 1v5 because their team didn't have the gold to keep up in fights. And Darius isn't really the best at lategame. If he can get in the fight he'll do some damage. But with very limited mobility and a long CD on his pull his ability to get into fights without assistance is very small. But that's expected from a lane bully.