I did coke but my husband doesn't know.
That's not good. Why would you do cocaine knowing you could be caught?
I like the feeling that being high gives me.
You shouldn't lie to your partner, and should come clean about your drug habit. Doing drugs can really harm a relationship and it is only fair to him that he knows what you're bringing to it with these illegal substances. Talking through this issue may be a good first step to healing your relationship and your bad habits.
I won't tell him. We are separated but he won't want to get back together if he finds out.
If you are planning on getting back together, you should be honest with your husband. It would not be a good restart of your relationship if you start hiding things right from the start from your partner.