According to Dr. Phil, there are several complications associated with loving a married man, including the possible development of a lack of trust. If he lies to his wife, it is always a possibility he is lying to his mistress as well.
Another complication with loving a married man is the potential pain the affair may cause his wife. She is an innocent party and the one the man made vows to, and she made vows to him. If he would cause this type of pain for his wife, it is possible he would eventually cause the same type of pain for his mistress no matter how much she loves him.