Sorry to hear of your travails.
I've been there also, and many have offered good advice here.
Mine was a blindside for me. Married 20, active in church, adopted a son, in my mind we were a for-sure forever thing.
No, at the 20 year mark she drops the bomb, discovered later she was cheating with a married guy at our lake home location. He and his wife had just split since he'd dropped the bomb on her.
Terrible time for me - got to learn more about clinical depression than I ever wanted to know.
Unfortunately - my church family was of little help. Small, sorta country church and I no longer fit the mold there, which was married, with 1,2, or 3 children. Best I could get was a mumble and a handshake.
I eventually left and joined a nearby larger church with a much more diverse demographic. Much better.
Married friends who'd been together forever were also of little help. Like me - they couldn't even imagine.
What helped the most was advice from guys who'd been there (kinda like those chiming in here), and staying busy enjoying the things I liked, mostly being in the woods or on the water.
A fellow Detective I was working with (he'd gotten the t-shirt) offered what I learned was good advice - and that was to 'be good to yourself'. You have to remember that right now, no one else is going to do that. Nothing extravagant - a new shirt here and there, a book, a gun you've been pondering, whatever. I found that really helped.
There was mention of 'DivorceCare' offered at local churches. I availed myself of that and got to meet some really good people that were hurting just like me, as well as people who really were called to be of help.
In dealing with an 'exiting ex', I learned to interpret phrases she'd use (stuff I KNEW was not of her invention) as we went through the process.
Absolute #1 was her use of the word and term " F A I R".
Do not believe that that word has any implications for you. That word simply translates to what is best for her. Period. End.
Let me know if I can be of any help. You will see it getting better, but it's gonna be uphill for awhile. But, it does indeed get better.