AFWAW, PDT is right...this would have been a good time for her to realize what she is losing by not being able to call you and D whenever she feels like to ease her loneliness and have someone to hang out with. I know it is easier said than done but try not to let her spend the night at the house again unless she has moved back and ended everything with OM. I hope for your wellbeing this is over before Oct.
Anyway, what is done is done...this is a good opportunity for you to spend time together as a family with the understanding that Tuesday is the day that you cut all contact with her unless it is about your daughter and then email is fine unless it is an emergency...no more lunches, overnight visits, supper, chatting on the phone, emails. This serves a couple of purposes...it lets her know that she has a family she can return to now and lets you regroup mentally and heal yourself. It will hurt and at times you will feel like an addict in withdrawls...go for a run.
It will get better...continue your investigation. It is more important than ever that you expose and end this affair. If you can afford it get a PI. You can save money by letting them know when you think they are meeting...for example if your daughter is there she will not meet him on x-day (I hope).
Time to reschedule with the lawyer...did your wife discuss the D at all? Review any paperwork? What will she pay towards CS?
You did well this weekend...if your D wants to come home let her...do not get caught up in trying to please your W by making your D stay with her. Let her feel the pain of poor decisions...do not sitdown and have a friendly chat about the D...get a lawyer. The only thing you want to talk to with her is fixing the marriage and taking care of your daughter.
She has come very close to giving up her moral authority to be a parent or your wife.
Again, recommend you have a good time and use this to prepare yourself for what you need to start doing on Tuesday. The longer this goes on the more difulcult it will be to fix.
