Yes she has to take responsibility for her part in the breakdown of the M, six of one and half a dozen of another as we say in the UK. Having said that like you I feel that I’m more than 50% responsible, my H agrees with this and believes it’s all my fault.
Difficult to say how long to hold out before you come to the conclusion that you wouldn’t reconcile, think I might be at that point now, I’m considering D. Maybe if you’ve got to the point where you wouldn’t be at all interested in ML with your W? Or if you felt that you couldn’t get past what she’d being doing without you or the fact that she’s been unfaithful. How long you wait is a very a personal choice.