Perhaps it's time that you acknowledged your own emotional limitations and set the boundaries of what you can live with in your relationship. Although you ask the advice of others with an open mind, ultimately, the answers that you seek resides entirely within you. No one can step into your shoes, relive your life experiences and your time with your partner, and fairly or even plausibly make a rational decision as what you should do in this matter.
Decide whether you can live with an open sexual relationship or whether you can only live with a one-on-one partner. Discuss this with her and make sure that both you and she understands your limitations and what you are willing to live with. Should you decide to have children with this person, whose children would she bear you? Would it matter? What is the deal breaker that would make you walk away from the relationship? Has she crossed that line already?
Another thing to think about in making your decision is which one of you holds the most influence or control in your relationship. The person who has the most controls is the one with the least amount of interest in the marriage. Obviously, that is not you. You have been doing whatever you must to keep it together, even letting her have an extramarital affair. You want to keep it together, and your wife just doesn't care. She is pulling all the strings and you are just following along. It is your decision to let her have the affair that brought you to this point.
You said, "It not her having sex with other people i mind its the decline in our relationship that results from it." Regardless of how you phrase it, it is the extramarital affair that is causing the problem. All of that being said, it honestly sounds as though you are looking for someone to tell you that you should walk away. Perhaps, you have already made your decision and are just afraid of moving on. As watasch advised, "I believe you knew the answer to your question before you posted it here. Listen to your gut. If it hurts, get out." Even grm hit the nail on the head, "If you really love someone you don't want to hurt them, it sound to me that she no longer loves you, even if she says she does."
Whether to stay or to walk away from a relationship with someone you love is probably the most difficult decision you may ever have to make in life. It is not an easy one and if you do decide to walk away, you may spend a very long time in mourning. With indecision, perhaps you should consider some very serious marriage counseling before taking that final step.
Good luck, my friend.
« Last Edit: April 28, 2013, 07:11:36 PM by DrWoody »
Upon returning home after a lifelong absence, you may find that the journey back was more impressionable than the arrival, and those you met along the way have already shaped your future.