As for the cub scout thing -- I think it was time for you to step aside. It is VERY normal for ex-spouses not to want to be around the X. You should not force her to choose between continuing your son's normal activities and doing what it takes to avoid you. The kids come first. It was her night and son's scout night -- your stubbornness cost your kid.
Regarding trying to make progress on custody -- If your problem with letting go of the 10-mile limit is that you think this will allow XW to move in with OM, then I'd strongly recommend that you accept her terms if they are otherwise reasonable. You can't control your XW's LL or how much your kids are exposed to her BF.
On the other hand, if you have another concern about giving up the 10-mile limit, then perhaps you can address it directly. "I am willing to give up the 10-mile limit if we specify the boys will stay in the same school, not have an average commute to school more than 45 minutes one way, be available for scouting activities, etc..."
It is not going to do your kids any good to drag the custody issue through the courts, especially if a reasonable compromise is within reach.
My mediator told be -- no D agreement is fair until both parties feel screwed. This has proven to be very true, and I expect it holds for custody agreements too.
