If I talk with my boards on his misbehaviour it will get them stressed and stop believing on the company
Sorry dude, looks like that is precisely what you are going to have to do. Don't worry about the board stressing; they can handle it. That's their job.
Focus on YOUR job: the success of the company. The board will stop believing you when you prolong this longer than you should have, actually making the situation much worse.
When you go to the board, GO PREPARED. Assume the board does not know anything. And treat it almost like a trial where you will get to present your side, and at some point, your co-founder will get to present his. In these cases, I like to open up a document and put down the facts in bullet points. When presenting, remain calm and stick to the facts, which when evaluated by a sensible party(your board), should have them arrive at the same conclusion as you.
Sorry dude, looks like that is precisely what you are going to have to do. Don't worry about the board stressing; they can handle it. That's their job.
Focus on YOUR job: the success of the company. The board will stop believing you when you prolong this longer than you should have, actually making the situation much worse.
When you go to the board, GO PREPARED. Assume the board does not know anything. And treat it almost like a trial where you will get to present your side, and at some point, your co-founder will get to present his. In these cases, I like to open up a document and put down the facts in bullet points. When presenting, remain calm and stick to the facts, which when evaluated by a sensible party(your board), should have them arrive at the same conclusion as you.