If I were in your shoes, I would not say anything at all, and let him do all the talking. You need to hear all the "evidence" against you first. You may start denying things he didn't even know about before, and get yourself into deeper trouble -- or fired.
The key point to me is that he didn't fire you already. That tells me that:
- He may have suspicions about you, but is not sure.
- He doesn't think it's a fireable offense at this point in time, but may be waiting to see how you handle it.
- He is going to fire you after he gets someone else lined up to replace you.
If he has pretty good evidence against you, then I would just fess up and then downplay it as a very stupid one time mistake that has never happened before, and will never happen again.
I hope you've been preparing for possibly passing a drug test, and that you've been proving (every day) how indispensible you are to the company. He may have one reason to fire you, you need to make sure there are a lot more reasons why he should not.
The key point to me is that he didn't fire you already. That tells me that:
- He may have suspicions about you, but is not sure.
- He doesn't think it's a fireable offense at this point in time, but may be waiting to see how you handle it.
- He is going to fire you after he gets someone else lined up to replace you.
If he has pretty good evidence against you, then I would just fess up and then downplay it as a very stupid one time mistake that has never happened before, and will never happen again.
I hope you've been preparing for possibly passing a drug test, and that you've been proving (every day) how indispensible you are to the company. He may have one reason to fire you, you need to make sure there are a lot more reasons why he should not.