Well you are getting past the hump meaning denial. You are starting to understand the enabling both you and his family have done in the past. It's ironic how he used his coke addiction as blame for his sexting. I guess he figured one (sexting) was worse then the coke addiction in your eyes. OK so now you have to seriously consider whether this person is worth the well being that you and your son can have at this moment.
You are not to blame for his addiction, the fact he had smacked you around or him making the decision to messed around on you and the nasty lies. What you will be the blame for is allowing this man back in your home. So now you have to start thinking positive if not for you but for a child who cannot defend himself. You are his role model so you have to act accordingly.
He is out of your hands and in a higher powers. You have your own crap to deal with now so I recommend venting, counseling, bring in the best friends and family and have a serious B**** session the more support you have the better you will cope and of course we are here.
I am not as enlightened as the rest but I like to help if I can.