It took several years for me to get so unhappy I couldn't see a future with XH, then a further 2 years before I plucked up the courage to have The Conversation.
Years of gradually feeling more and more like the paid help, rather than a beloved wife. Of being belittled- not outright, but in small ways, like him never believing any facts I told him (sounds weird I know) without back up from Google or his parents. Even of being farted at, repeatedly, constantly, and extremely noisomely. Just generally being disrespected really.
I must admit, I went in to The Conversation a bit blind. I basically worked out what the worst case scenario would be (benefits, living in a 2 bed flat) and decided that yes, I could take that over the alternative (living with him).
It didn't turn out anything like as bad as I expected, which is, I admit, partly due to XH being fairly reasonable about things (apart from allowing it to drag on for 2.5 years).
If I were you, I would stick it out til after the public exams, but use that time to sort out solicitors, decide on what your personal line in the sand would be and so on.
How kids take divorce is 100% (imo) down to the parents. They will be upset, but if you don't bitch about your ex, don't drag them into the whys and wherefores, and don't try to force them to take sides, they'll come out of it fine.