I encourage you to ask yourself why the cheating is more of a deal breaker to you than the drugs. And believe me, I'm not judging- I've been in your shoes. It took me finding out about my ex's affair to finally see the light. But looking back, I think that's really sad.
I find it really disturbing that he is telling you he's only meeting up with escorts to score drugs. Yikes! That should be even more of a red flag than seeing escorts.
I agree that you're being gaslighted. None of this is acceptable. Please be careful. You are not safe. I know you think you know this person, but his addiction is the one in control at this point. You are not safe.