I think coming on a forum and asking these types of questions for a matter of opinion is the silliest thing you can do.
First, are you married or just dating this person? Are there children involved? How many years into this relationship did this happen? There are so many issues to be looked at before anyone can give any kind of response with any kind of intelligence behind it. I am amazed how many people will say “LEAVE” “Once a cheater always a cheater” and not take anything else into consideration.
You say you work a lot and maybe he waited for your attention and it never came. This is what lends him to be attracted to somebody else and have an affair. Where there warning signs? Did you miss them? Do you even know what they are? Did he ever seem disappointed that once again he fell second to your career or other things in your life you put first? Or was it just for the thrill? The strange? The sex?
I’m not judging you, I don’t have that right, but there are so many factors involved and many self help books out there on the subject to walk you thru the decisions. There are so many other forums out there with many more people much more educated on the subject. You can read about those who had the affair and the ones who found out about it, both offering insight on the subject that you will not find here.
Good luck