I am sorry to hear that your bf cheated on you when you two are still together. I understand that feeling sucks and you are so pissed of right now you want take it out all on him. The pain, the agony that he caused and all that time you wasted thinking about him. How dare he! But, deep down I can still tell that you cared a lot about this guy despite since you have been separated so many months ago but still unable to move on.
I think that you should channel your anger somewhere else - take up some sports, hobby or travel somewhere nice for a short while so you can calm yourself down and think properly. Taking it all out on your ex won't do you any good. It will just hurt both of you more and if you spill all his secrets that he be-trusts you with. You and him will also be in a very awkward and uncomfortable situation at church or work because you know words get around.
Revenge is sweet, at first...... But what comes next? What if he also plotted against you as well? The cycle of hatred will never end. Like some of the posters here said, take the high road and leave it be. He will pay his consequences some day. Who knows, maybe his other cheating bf also has another cheating bf.
Anyways feel to rant around here if it makes you feel any better as a lot of us here have similar experiences and are willing to lend an ear