On the assumption that this is real, I would say that the easiest thing in the world is for people to say you should not have done what you did and you deserve what you get.
That may or may not be true. But the situation is as it is and now you are pregnant. You can't turn back the clock and make a different choice, all you can do is learn from your mistake and move forward.
Your boss has basically used you as a blow up doll. You can't change that, but you can get a bit of self respect. Are you keeping the baby? If so, you owe it a decent life.
He won't tell his wife. This is not unusual. Most married men who seek sex elsewhere do not want the scratching of this itch to impact on their real life.
His wife has done nothing to you. She is his victim and to a lesser extent, she is your victim too. Should you tell her? No. He should. Will he? Not until or inless the CSA comes after him. At this point he will inevitably insist he is not the father, tests will follow, it will be messy.
Anything that happens to his marriage he (and probably his wife too) will blame you for, so be prepared for them to turn on you.
Unless she throws him out, at which point he will 'choose' you and arrive on your doorstep with his shredded clothes in a bin liner, telling you how much he cares.
Your job now is to put the baby first and to assume that you will get nothing from him but grief.
Good luck. You will need it.