Dong Zhou wrote:Yes Lu Bu was as selfish and filled with ambition, unlike the other he didn't have any real political nous and was far too erratic with his loyalty. Lu Bu had helped Dongy control Xian, I suspect his betrayal there was because he feared for his life.
It could be a multi-faceted event. Previous to his death, Dong Zhuo had threatened Lu Bu with physical harm. Although the Diao Chan plot didn't exist, I believe Wang Yun still had a hand in the assassination, mainly the part where he convinced Lu Bu to do it. This physical threat was the focus of that piece.
Also, Wang Yun held an edict written directly from the Emperor. Certainly, even if he didn't have full loyalty to the Emperor, he felt the time was then to take advantage of it.
Not to mention the military and political gain he would attain from such an act. Killing Dong Zhuo would mean he would gain Chang An, a venerable fortress, and the leftover military of Dong Zhuo. Unfortunately, this didn't matter since those inside the city let Li Jue inside Chang An...
I look at Lu Bu as a simple minded man. He does what he feels is best for himself at that time, caring little for other opinions. Point in case, even when he looked at the big picture and sought to ally with Yuan Shu, he defied everyone else's advice. That is, of course, until Chen Deng convinced him otherwise.