There must be a lot more to this story that will come out. From what I read, Udoka did a great job and the Celtics were high on him as their coach for the future. For what has been reported about the relationship being consentual, one would normally expect him to get a slap on the wrist but to keep coaching if the Celtics wanted it.
Either the Celtics wanted him out, which seems unlikely, or ther is more dirt about to be spilled.