In your shoes my marriage would be over. My husband know this, he didn’t do drugs before meeting me so didn’t have to stop anything, but I made it clear that it was a boundary that I would not be prepared to have him cross. It sounds like you have done said similar in the past, if you have then I would stick to your boundaries.
Can you speak with your in-laws about his drinking and drug taking? In your shoes I would arrange for your in-laws (or your own parents) to be there for any contact. You deserve to be loved and respected and prioritised! Your babies deserve to be their Fathers number one priority!
I hate to suggest this, but it is very likely that your husband has been either having an affair, or had his head turned. All of it sounds like a skirt chase to be honest and reads very much like the script! I’m sure there must be a website somewhere, advising men what to say when they are cheating on their wife! Unfortunately cocaine and sex tend to go together, it could be that whoever he had his eye on has rejected him once she realised he was turning into a drunken drug addict. Or perhaps was also in a relationship and didn’t want to leave her partner.
For the above reason, I would be reducing your contact with him as far as possible. Which is why I would try to arrange for your parents or his parents or even a friend to supervise contact.
I wouldn’t entrust my precious babies into the unsupervised hands of a drunk on a comedown.
I would move on mentally. You don’t need to start dating, but do things for yourself! Go to the gym, get your hair done, buy yourself clothes that you feel good in. You are Mummy to two little ones and it’s easy to lose yourself and become Mummy. Discover you again, if you have a babysitter then go out with your friends, or take up a new hobby. You have been part of a couple and then Mummy for years. It’s time to be @Lashes5687 again and find out what that means, what you like, what you dislike, what your boundaries are, and who you are apart from being Mummy or wife.
Once you have done this, you can then make a decision about whether you give your ex another go, or you move on. There is no hurry, but don’t let him hold you back - my guess is he will panic when he sees you rediscover yourself, he will likely assume you are seeing someone and might even turn nasty out of jealousy. Don’t let him make you feel any guilt- his behaviour is appalling and he doesn’t get to dictate to you what you wear or who you see.