For a moment imagine possible developments. He favors you with care and affection, because with you he will get what he apparently lacks in his family. But sooner or later this relationship will lead to misunderstanding, because each of the favorite women married men will "pull the blanket over himself" and, therefore, become more demanding. And the man will likely prefer to get rid of one of you. It is likely that the cast will remain the mistress, since you and him are not linked to any obligation.
To avoid this, suppressing thoughts about him even before the emergence of real feeling. Try to focus on his negative qualities. Remember all the details. Maybe he puts too much gel on the hair, or he pulled the silly face when he's surprised? Even these minor things will help you "sober" look at the object of desire. For greater effect, list your positive traits and charms of nature. Often keep in mind the imbalance, and your interest in it will fade away.
Take all the time, so there was no space for thoughts about a married man. It is helpful to immerse oneself in work or engage in a favorite hobby. It'll help distract you and might cause a new experience. Just imagine you well, and fruitfully done, received the praise of his superiors and a cash bonus, then went to the beauty shop, or on a journey. If you perfectly will spend time, your happy look will attract more interesting men.
Don't be a recluse and don't beat yourself up over your choice. Love is unpredictable, because no one in advance can't assume who gets an arrow of Cupid. Better stay home, spend time with friends, do not be afraid to make new friends and not lose your optimistic attitude.