In a court of law, bias is not supposed to be present. If they were both married, yet having dinner, they could be friends or the prosecutor is trying to get on the good side of the judge (or they're cheating). If you feel that the judge might not make impartial or fair rulings then it may be best to try to request him to recuse. However, it would do good to have evidence of such belief and not off of suspicion. The main goal of your case is to try to get your client as little time, or no time, in prison, so doing something that may cause prosecution is not favorable. It may also be helpful to look at past cases, or ask people who have worked with the judge before, to see if he has ever seemed prejudiced on any cases. Try to make a choice based on what you believe and feel will have the best outcome. Remember that this case can determine your clients future.