I don't think you are going to find the answer here, as some wise mumsnetter said to me recently we are just strangers on the Internet, and knowing that how could we tell you what to do with your marriage, however i imagine you are looking for outside opinions that may help guide you down the right path.
What kind of evidence do you have to make you so sure he cheated?
I am not saying he didn't but i am sure you would want to be 100% sure (i know you say you are) before you make such a life changing descison
Also are you prepared that you may have to get a job, or go through a huge life style change if you do separate/divorce?
Again this is not me saying don't leave him, but more think about what your choices are if you do.
Do you love him?
Are you prepared to forgive and forget to wipe the slate clean and move on from this or is it over for you and you just want to move on from this alone?
I personally wouldn't forgive cheating, but i would need a confession or proof, before i made any decision, however we do not have kids at the moment, so for me it would be easier to just leave.
There are clearly lots more points to think about, however these are a few to get you started.