Good question, Aren't you going to ask her to choose first and then gauge your actions based on that?
Formulate a plan, always have a plan and make sure you have thought out what's going to happen in either scenario.
If she chooses you, you continue going to marriage counselling, she continues to go to her personal counselling, she agrees to cut off all contact with OM and she agrees to be transparent with all of her actions so that you can both build up trust & respect in this relationship.
What is her current strategy for dealing with her sexual abuse issues, it definitely requires therapy but successful therapy is not long & drawn out, in fact it's quite the opposite, anything that is more than a year in it's scope won't do any good speaking from personal experience.
If she chooses the other man or can't make a decision, you have to determine what you have to do. No one can make that decision for you: do you continue to tolerate this open relationship because you love her and want to keep her close or do you finally put your foot down and say enough is enough. Either way I wouldn't leave the home - I would personally ask her to leave if that would be your plan, in fact it's what I did at my end. I packed my wife's things for her and put them all in the minivan and told her to go live with her parents because I didn't want to share a home with her anymore. In my case things didn't work out for her, the grass wasn't greener, the affair ended abruptly soon afterwards and she was left without him & me, she had a bit of a wakeup call. We have joint custody of the children but I tend to have the kids 80-90% of the time now, it's been like this for quite some time. She was living with her parents but she ended up fighting with them as well, it was funny, they actually grew tired of her childish, immature ways because she started treating them poorly and they kicked her out as well - she ended up burning alot of bridges with family & friends.
Sometimes they need to experience hard times & maybe hit rock bottom before they see that what they've done with their lives - it's a bit of a wakeup call. They've been pursuing a fantasy life all this time and sooner or later, most find out that fantasies are just that, fantasies and they don't last. The affair can't continue to remain new & exciting, it becomes old, it loses it's lustre. Losing the security of their home & previous life makes them fend for themselves, they don't have the luxury & security of their old life while maintaining their affairs. Having children means they have make time to continue being a responsible parent, until a separation/divorce goes through, they have to rely on their financial resources to live and that means their current lifestyle is impacted and you don't have to make that easier on them. There are consequences for our actions, we're adults and we have to learn that. When they realize that the new grand life they had been planning is a bust, they start to see the errors of their ways and start to reconsider reconciliation. Another example, check out smileyperson's thread, that's where he's at right now, he has realized his value, he is separated from his wife, her affair ended, SP moved on with his life, he's having a good life now, not just surviving, THRIVING!
That's where I'm at currently, my wife is asking to go out for coffee, taking me out to restaurants, going on dates and I'm not making it easy for her, I'm not just going to say ok, that's good enough for me, come home, let's be happily married again. Trust has to be earned, because it's been totally eroded, the changes I'm seeing in her have to be real, not temporary for short term goals & rewards. If our marriage is important to her, she'll put the effort into showing it and do the work that's required as there is alot of damage that has to be recovered from.
I also don't want the marriage I had because it's what led to this state we're currently in, I'm working on myself and I definitely want a better life for myself and my children and my goal is to continue pressing forward, realizing more of my untapped potential, continuing to grow & evolve and be the best me I can possibly be and that's the goal for everyone, especially the DBer's on this site.
Your goal ultimately is to have a great life and to set an example for your children so that they can emulate this behavior and have great lives of their own - that's your legacy as a successful parent and human being.