Hi Laura. Not a good situation to find yourself in as it looks like he has not given up the dreaded stuff.
You know the score, lying and paranoia and turning it on you accusing you of cheating. Sorry but he is cheating on you with the cocaine.
If he wants to be clean he will only be able to do it by himself. You cannot help him. You can just be there if he does get clean but not during. Its hard but you have to think of yourself, your children and now your unborn.