Ok let’s say you said that and she didn’t care. How does that change the situation your in right now? Either way she’s still with OM right? But one way you stick up for yourself which again communicates that you love and value yourself and you are not willing to share her with another man.
You can’t nice your way back. You also can’t turn a blind eye. Read Chris73s thread or PEW1974.
Look man I know this is hard but things are going to have to get worse before they get better.