Has she filed for D yet? A "trial separation" sounds like uncertainty.... perhaps wavering? Maybe waiting until she feels more secure about the situation with OM before committing to a decision.... and that's certainly much easier if she still has you as a back-up plan.... especially if she thinks you don't know about OM....
If you do confront, make sure you do it nicely without blame or without villifying her. I would be matter-of-fact and give her A LOT of space. Definitely GAL big time. She has to understand what it's like to "lose you." And at the same time, you have to be so wonderful (supportive, a great listener when you are together, emphasizer, the best dad ever... etc...) that if she decides to leave she'll eventually realize she has left someone she can never replace.
There is no arriving, ever. It is all a continual becoming.
