He told her it's okay for her to go out with Brent. Which is hardly some sort of character-defining event, certainly not to the point of extrapolating that into poor decision making somehow being his calling card.I disagree. He encouraged Nikki to date Brent. I expect most people to do better than that, even if they lack confidence and harbor a secret crush.
"Yeah, why not, go out with him" doesn't mean he told Nicki to become Brent's girlfriend or even date him more than once. That's all Nicki's own decision making.