I dont know if anyone else is involved or not. I've tried to investigate and all I found were texts. I know the ex boyfriend is back in the picture as they are talking but from what I hear, he is still with his g/f of many years since her.
I do not believe it is appropriate for a M woman to have private/personal TM, IM, calls, etc. with OM. And if she's making contact with her old BF then that is another A--you can count on it.
Don't be blind about this. She wants OM for romance and to have you to fall back on in case the other doesn't work out.
I don't think that being her "friend" while she is unfaitful to you is going to win her respect. She obviously doesn't respect you or she wouldn't be looking for another man. Each time you crawl on your hands & knees begging her and trying to convince her that you've changed....it causes her to lose more respect. You are telling her (by your actions) that you are willing to live in an open M. A desparate man is willing to put up with anything, right? Are you that desparate?
You need to know what your own boundaries are before you can tell them to her. What are the deal breakers in this M? How long are you willing to be a doormat? Nothing pretty in that picture.
Get your head out of the sand and face reality. Your W is hung up on another man. The only chance you have to get her back is to start acting like a man she would desire. What you've displayed so far isn't it! I can tell you this...she doesn't want some weak sister pleading and making promises when she knows who has been the unfaithful one in the M. She wants to see you stand up to her and have some dignity & self-esteem. She wants to see the man she fell in love with.
She may kick & scream in the beginning, but she truly wants you to have boundaries for her to honor. Lay those boundaries out there and if she doesn't respect them.....it's time for the consequences to take over.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!