Xebec will kill himself
Bitchmu can't defeat Xebec so she resorts using Domi Reversi on him
Knowing that he can't control his body movement anymore and he starts attacking Eris and Teach, yet he still has conscious left, Xebec will try to kill himself
Whitebeard and Kaido not sure what to do but Xebec also ordered them to kill him. Reluctantly Whitebeard and Kaido also attacked Domi Reversi Xebec thus "the betrayal".
Kid Teach saw it, misunderstood and thought Whitebeard was really betraying his father.
That's what really happened
@Akai2 @Blackbeard