First of all, welcome faithhopelove - and good for you for reaching out. You're husband does sound like he needs some psychiatric help, or a good smack upside the head.
I'm not a doctor, but I am a wife of a bipolar man and I can tell you - from his own mouth - people who are bipolar know what they are doing. He once said that he knows what he's doing, he just lacks the ability (or willpower if you will) to stop it. I can also tell you that my husband has never hit me OR cheated on me, and we went through some really rough times... so for that my dear, I will tell you there is NO excuse.
I commend you for taking him to marriage counselling and if there is history of mental illness in the family then it is quite possible he is in fact bipolar but only a pdoc is able to properly assess that.
Ask yourself this: after what he has done to you (cheating/hitting ), if he were to get help, would you want to stay with him? You need to remember that this roller coaster doesn't end. There will be good times that hopefully last longer then the bad, but if he's not willing to even accept the diagnosis of bipolar, you're ride with him will be worse than others. My husband turned to self medicating with drugs and alcohol for months and spent more money than we made (including getting a $15,000 loan to start a business that never happened). But I can tell you that in those months, had he cheated on me or lifted a finger towards me, there would not be any chance for our relationship IF and WHEN he did seek help. Now, I can't speak for you and I'm sure you still love him, but now you have a child to think about... and it's not about you anymore. I only say this because of you saying he won't see a doc or admit to a problem, so if that's the case, there isn't much you can do. I'm sorry you're going through this, but know that by coming here, you are not alone. ((HUGS))
"Twenty years from now you will be more disappointed
by the things you didn't do than by the ones you did do."
-- MARK TWAIN