Be practical about the arrangement and don’t allow your feelings to run amok.
Always wears a condom to protect yourself from contracting STDs.
Chances are that she will cry her marital woes in front of you; how her husband mistreats her and how her in-laws are unfair to her.
Over the course of our marriage, I've seen her interest in sex decline gradually to the point where she doesn't even have an interest anymore.
I treat her very well, provide most of the financial responsibility of our household, and make sure that I continue to take her out on dates, buy small gifts for her, bring her flowers, etc.
The man will come after you and have at least one show down with you.
Nothing hurts a man’s ego more than his wife sleeping with another man.
More often than not, the relationship will lose its steam when the sex gets repetitive and boring and she will move on to someone else (or return to being faithful to her husband).
You are her second option and don’t daydream about her divorcing her husband for you.
But in spite of all these efforts, when I try to initiate sex, my wife participates through the foreplay and then tells me that she just doesn't feel like having sex or is too tired.
She still enjoys kissing and receiving massages from me but that's as far as it goes.
I also make sure that I share equally with the household chores and cleaning.