If OW is considering a PA with you then she is not a "friend" of your W. If you are considering a PA with OW then you are not a "friend" of her H.
Friends do not take action that will hurt each other and believe me ALL FOUR of you will get hurt. You are going through some things in your marriage right now that are causing you unhappiness and pain but if you want to stay in your marriage please try everything you can before you look outside it to "solve" your problems.
Have your read DR or The Sex Starved Marriage?
You will find understanding and support here BUT you will not find justification for having an affair EVER