If you manage to have an intimate relationship with a "married guy", moderate your feminine curiosity – don't try to see her to see if she's prettier than you, smarter or skinnier. Of course, the presence of a rival is a very powerful incentive for improving self-esteem, but nevertheless...From what you will see and I am pleased to say that it is less attractive, nothing will change. After all, you know that, despite your superiority, every day he returns to her, share with her the same bed and shared the bread. So something keeps him with her. This feeling sooner or later you develop an inferiority complex, you are always going to be introspective on "And yet- what is this, why is she better than me?".
Moreover, do not search for meetings with the wife of your beloved. Why should you? To talk, to open her eyes to her husband with hope that he'll marry you when she file for divorce? Look at things realistically – if he left his wife in the first few months of your relationship, is unlikely to dare to do it. Surely he can think of a lot of reasons: small children, the overall business, a sudden illness of the wife... Who wants - searches for possibilities who does not want – looking for reasons. Think about it. If he wanted to break up with her, he would have found a way to divide business and to explain to children. He just loves her much more than you do, and you will have to live with it.
If you are familiar with your partner's wife, don't try to get her best friend to "keep their finger on the pulse" and know about their lover all. To decide on such an act can only be a very mean person who doesn't care about questions of morality and morals. Imagine what will be her condition, if she accidentally finds out about your intimate relationships? Her husband's mistress, every day I pretend is her best friend, found the strength to look into the eyes of the husband and where she sleeps.