I disagree a bit with some of the previous advice. Given his erratic and financially irresponsible behavior, you need to protect yourself and your kids financially. That may require a legal separation or a divorce. You can always get remarried to him but you may not be able to recover from financial ruin.
As for him "finding" OW three weeks after bomb drop - sure, it's remotely possible, but the odds are 100 to 1 that he started an affair with her BEFORE bomb drop. Not that it changes much in your current situation, but you should know that is almost always the case and get yourself checked for stds.
Now, about the drinking. Did he ever have a substance abuse problem of any kind before? Does anyone in his family? Does anyone in his family have bipolar disorder? Has he ever had depressive episodes or mildly manic episodes before?
I ask because going from a minimal drinker to a heavy drinker is odd behavior even for a MLCer. But someone with bipolar disorder might turn to drugs or alcohol in a manic phase. On the other hand, if he has a history of alcoholism or substance abuse this could just be him falling off the wagon.
See an attorney just to learn what your options are for protecting your financial interests. It might be worth filing in order to protect your share of joint assets before he pisses them all away.
Meanwhile you can be kind - he sounds troubled - but get on with building your life into what you want it to be. This can be a time of great personal growth if you allow it. Figure out what you want to do that being with H was keeping you from pursuing, and do it.
