My divorce was like removing a band aid, it was done fast and hurt like hell for a short while.
I came home from working 3rd shift and decided to make her breakfast in bed. I moved her purse off the counter and saw a yellow form from legal aid sticking out of it, it was forms to file for divorce. I went in the room to ask her about it and she said she wasn't happy and didn't think I would want to do therapy. I told her I did and we worked on things. It was decided we would spend most the time together but I would set her up in her own place while we were working on things. Got her a tiny apartment (kids stayed with me) and got her some cheap furniture. Her first night over there she was texting me saying it was weird and she missed me, things looked like they were going to eventually be okay.
Then my buddy who was her neighbor told me some guy was over there at night, a few days later I called her and told her obviously this wasn't okay if we were going to work on things and she told me he wasn't going anywhere as she had put him on the lease. A month later she was pregnant with twins by the guy, come to find out they had been "together" since Christmas and it was now April.
The kids stayed with me until early October when our speedy divorce was finalized. She got physical custody as kids are better off with a mother we got joint legal. I lost everything...my house, my car until finally I moved 4 hours south to start over in Minneapolis. All I had was a junker car, my tv, two suit cases and my cat. I later sold my TV to buy Christmas gifts for my kids as it was their first Christmas with the divorce and I wanted to make sure they got at least a couple nice gifts.
Anyways...I didn't have time to "imagine her with another man" because she already was. My first revelation came on Thanksgiving when I was alone and was eating a Turkey TV dinner. I realized stewing in self pitty and sorrow wasn't going to provide for my kids. Them seeing me a wreck wasn't going to do them any favors and I wasn't going to give my ex the satisfaction of seeing me struggle.
I didn't have time at the beginning to drink myself into a stupor because I had my kids and needed to care for them, that first month I was down in Minneapolis though....it was bad.
It gets better though. Being apart from you kids never does, but the divorce itself does. My ex is still with that same guy 6 years later. My kids call him dad, they call my daddy. When they first started referring to him as dad (my ex made them) I was torn up about it. Until my oldest son, who was only 5 at the time told me "Daddy...anyone can be a dad, but you'll always be my only daddy."
That shit nearly burst my heart with pride and love. I never expected such a thing to come out of a 5 year olds mouth but until the day I die, I'll always remember it like it was yesterday.
Anyways, this got pretty long. My point is, even though shit is going to get even worse for you than it is now. (and believe me, it will) it will get better. And I know everyone is telling you that and you let it go in one ear and out the other...but it's true. And the more bullshit you deal with and put up with, all that means is that you're that much closer to things getting better.
In the end, all that matter is your kids and your own happiness. As your kids grow they will also want you to be happy. Be strong for them, be there for them, don't bad mouth their mother and set misinformation strait that they receive from her. (if they do) Don't be a dick about it, don't do it with anger or trying to turn it around on their mother as her fault...just be there for them and assure them that no matter what has or will happen...you're always going to be there for them and will always love them.
Also, my daughter was only 2 when we split. She has absolutely no memory of ever living with me and has been raised and lived with another man who she known as her dad as well...yet shes a daddys girl. I don't spoil her, I don't buy her shit all the time...or even often really. But I call her, I talk to her and when she's at my place we sit and read, watch TV, play games and she tells me stories and we have a connection that is uncomparable to anything else in this world. The dude she lives with she doesn't have any connection to, she doesn't even like to sit near him. It pisses my ex off to no end.
You do things right, your relationship with your son wont suffer, it'll just be different than you envisioned when he was born. And that's okay.
I promise, it and everything else, will be okay.
(sorry for the length of this and I hope it wasn't too boring or shitty to read)