Someone's personal moral obligation to someone else does not bind you at all. You cannot be culpable for him/her breaching it. So far as you are not forcing someone married into sexual intercourse, the person has free will and outmost personal responsibility for his/her actions. Thus, you cannot breach a moral code since there is no moral obligation binding you to refrain from touching the married person. The latter is bound but it is purely his/her responsibility.
It is not your responsibility to prevent another person from committing adultery any more than it is your responsibility to prevent a vegan from knowingly sharing a beef burger you have cooked, or preventing a Muslim from knowingly sharing some of your wine, even if these things could cause distress to their friends/partners if they found out. Their belief system is theirs to maintain or change as they wish.