The foursome reportedly partied at a dingy looking nightclub in Washington. Looks like Kendall is marking her territory (those rumours have been ongoing). She will just continue to show up in all the same places as him.
The urge for her would be stronger now that he is single and not having to worry about any backlash for splitting up a happy home. Not that going public with Kendall would help his career much. The Kardashians are so hated and I don't think his fans would approve. They didn't approve of Karrueche Tran either, but at least she was a much safer bet. I don't think he has reached that maturity level to have a serious relationship with a woman. He wants to dip his feet into as many different waters as possible before settling down and having kids. For now, he needs to be single for awhile. He has a lot more growing up to do.