By knowing she is cheating and not confronting or letting her know that you know, she thinks she's getting away with it.
And what I bet you are doing is one of two things:
1) treating her better in the hopes that she realizes you are an awesome guy and drops OM. In this case she's losing respect for you especially if she thinks that you know and that you chose to ignore it. You could be losing her respect QUICKLY and women cannot love a man they don't respect. Respect and attraction go hand in head.
2) you are treating her badly sometimes because you know what's happening and its eating you alive. This leads to passive aggressive behavior which is also a massive turn off for women. Leads to more loss of attraction.
Anyway you look at it, you are only helping her to lose respect for you and with it lose attraction for you.
You need to tip the balance a little. Don't do anything until you tell us here what you think you can do and how you intend on doing it. No shouting fits and no displays of anger.
Do you think she thinks you know? Do you think there is a reason that you SHOULD know? Like perhaps he calls her and she ignores the call when you are with her? Or something even more obvious?
Some women make it obvious in the hopes that their man will catch on. Any of this happening?
We need more insight as to what is going on.
Me, H-34 now 38 W-32 now 35 T-13 now 18 years M-6 now 9 Daughter 3 years now 7 Bomb 11/27/12 - OM 1 year in house separation Reconciliation 12/2013. Healed now 2017