I explained to her that we have a different perspective on what has happened, but that I don't entirely NOT get how she feels about it. I explained that, in any case, I forgive her. I then told her that my anger and vitriol is towards OM bc I think that he took advantage of her while she was in a vulnerable state.
I believe you are not being honest with your wife or yourself here. I am sure you may have anger toward the om, but I would also believe you have some unresolved anger at your wife on this issue. Maybe you are scared of telling your wife that "yes" you are somewhat angry at her for not ending the relationship with the OM and yes you may be angry with her for not coming out directly and telling you the facts and the truth about what REALLY is what is going on here...
I don't know how you can honestly forgive someone for something if you don't even know the facts of what is really going on to forgive them for. Bottom line is that they are STILL in contact. It is not coincidental that you just happened to be holding her phone when a text came in from OM. Obviously he knew about the birthday party...
Don't let your resolve on this allow you to lie to yourself or be naive about other things. You seem to be scared to get a little tough here and bring this to a head with the other man and her...
Women respect a man who doesn't share his women and is able to walk away from her if she tries to have her cake and eat it too.
She is either in or out. Either ends it with him or she doesn't. Nothing wrong with telling her to contact you when she is absolutely done with him because you have decided that you aren't going to share and aren't going to live in limbo wondering....
This isn't done with malice or anger or a sense of whining or moaning. It is done with confidence and integrity and resolve. Nicely yet firmly...
Women respond to that "stuff" really well... They have a hard time feeling the correct feelings for "wishy washy" men and men who allow them to play both sides....
Good luck
[edited by dbmod to add note: One man's good advice is another man's downfall. Some women respond well to this, a good deal of women go running. In general, this is NOT DB advice.]