Legal Question in Military Law in California

You probably could report him and he would be disciplined for "... conduct unbecoming an officer." But speak to your wife first to see what she has to say, whether the other man knew she was married, etc. Talk to the guy if you feel you can without blowing up. Speak to someone you trust showing them what evidence you have to see if they feel your conclusion is correct as you would not want to harm the soldier if you are wrong.