The limbo is the worst. Only you can decide when you've had enough. For starters, I would recommend that you do your best to show the world (and your W) that you are moving on without her. That means blowing up your GAL activities. You say you have your D most weekends. While its great that you have that and can work on being an awesome Dad, maybe you can take some time for you. Go on an awesome trip by yourself or with your D. If you go by yourself, that means D has to stay with W and screws up her plans with OM. Perhaps doing both is a good move.
Its true that most A's do go down in flames. With OM being such a complete loser, I have no doubt that will eventually happen here. Its just a question of how long you can wait. And then if it does end and your W comes back, you have to endure the mind F^ckery of knowing that your W chose this complete loser over you for however long it took. You would need to see some serious remorse to get over that one.
If dropping the rope and starting to move on with your life without your W doesn't work and you are tired of living in limbo land, the next thing would be to file for D. But if you do that, it has to be because your are truly ready to end your R and move on without your W. In the end, that's what it took for me and TxHubby. Filing is the nail in the coffin for limbo land. Many people are willing to hang out here for as long as it takes. But it is a horrible place to be. Only you know what is best for you.
Me: 48 y/o W: 47 y/o Together: > 20 yrs BD: Dec '15, then S 2nd BD: Mar '16, then I filed for D April '16: started piecing