I felt compelled to reply to this.
a few years into our relationship with a 5 month old baby I found myself in the same situation as you. regular cocaine use once/twice a week and I had no idea.
I kicked him out and ended our relationship. He went properly off the rails. He was useless at work, started doing cocaine nearly every night.
A few months later we decided to try again- I'd come to terms with the lies/betrayal. We started 'dating' but living apart. He went to counselling alone. We went to couples counselling.
We had the following arrangements which made it possible for us to be together again-
Everyone knew about it. I couldn't keep his 'dirty secret'. Friends, family, all were told about his problem. I needed support and after all the lies I wanted honesty.
I controlled all the money, and still do to this day. I get his payslips, bank statements, etc. Every penny is accounted for.
I brought drugs tests online. I needed to know that I could know for sure that he was off it.
He changed his number. Stopped socialising with those who also used.
And eventually we moved back in together (over 18 months later).
4 years on - I still control the finances, we both agree that cocaine is a weakness and if he felt that if he ever found himself with spare cash and after drinking alcohol he could be tempted. I still keep drugs tests in the drawer though I haven't needed to use them in years.
Its hard work. I never fully relax in social situations where alcohol is involved. I take responsibility for every penny of our money - I would feel it was my 'fault' if he one day had access to £100 and spent it on cocaine. It would be his decision to take drugs, but I would feel I had enabled it. I'm still not 100% happy with this as I know its not a healthy way for me to feel.
In my case he 100% wanted to change. He accepts that the financial side is necessary and he did everything I asked of him to prove I could trust him again. He would do a drugs test now if I asked- he doesnt complain or protest, he accepts that the situation is of his own making.
I'm not sure the trust ever comes back - I trust him with our children, other women, my life. But I know that a bit of white powder will always turn his head and I made the choice to support him in staying away from it.
Sorry very long...dont make any rash decisions. Its ok to feel cheated on, betrayed and angry. Its ok to ask him to get help and prove that he wants to change. But the age old CCC...you cant change it or cure him. He needs to do it with your support if you're willing to support him. If you're not willing to support him then thats ok too- its a long hard road and I'm not going to pretend otherwise.