Shoo--sorry to hear you are feeling down. You will go through up and down moods constantly when dealing with the trauma of divorce. One day you'll be happy, one day you will want to curl up in a ball and disappear. Sometimes both will even happen in the same hour.
There is no easy fix. No pill you can take to make the pain go away. It's a process. Time. Time and no contact with your ex (except for co-parenting) are the only ways to mend your broken heart. A lot of people will say "get busy!" and while it's great advice, sometimes when you are dealing with divorce, the last thing you want to do is be around people, faking a smile, engaging in anything, cause truthfully, you rather be at home hiding from the world. And that is ok, too. As long as you don't get stuck there, in that cycle.
Have you considered doing IC? Is there a place you've wanted to visit (even a town nearby) that you never have? A recipe you've wanted to try? A wine you've wanted to drink but never have? Are there old friends you haven't called/seen in awhile? Call them? Do something different, try something new. If you have a bunch of tv shows you've been meaning to watch, sit down one weekend and watch them. Get a new haircut. If you have a bucket list, make it your missionto cross one thing off soon, this year.
Your wife appears she has moved on to you-since she has OM lined up. But know she either was emotionally gone from your marriage long ago or she hasn't grieved yet cause the "infatuation feelings" she has for OM are maskingn the trauma of divorce. I honestly think it's really stupid for someone to go from something as serious lik ea marriage straight into a new relationship. But hey, to each their own. When the giddiness wears off for her (and it will, it always does), she will have to reflect at what she did and the pain of the divorce.
But that's not your problem.
Accept you will have bad days, and you will have good days and dust yourself off when you are feelinng down and stand tall with your head high.
They say you haven't lived until you've been through a divorce. And if that isn't the f-cking truth I don't know what is (LOL).
You'll be fine.