I can't comment on the logistics of a shared care arrangement with him being in the forces as I have no experience of that but wanted to back up the others in what they've said.
When DS's dad left me it was devastating. I remember telling my mum it physically hurt to breathe which sounds so melodramatic now but I remember it. It was like having a permanent panic attack and it was awful.
The good part of them deciding they're done is there is no back and forth. You have no choice and you can't be tempted by the pick me dance because it's done.
I sat and made a list of all the things I had wanted to do that I hadn't been able to do that exdp didn't approve of. Some big things (like I got my degree) and smaller things (dancing around like a crazy person with a glass or two of wine/having friends over/leaving the dishes until the morning/watching a sex and the city box set etc) and everytime I felt it get on top of me I picked something off the list and did it making sure I fully appreciated it was something I couldn't have done if he was still around without a lot of sulking or an argument.
With regards to learning to let your kids go for access:- it's tough. They've been your whole world since they were born and you've more than likely never been away from them for a long stretch of time. It's an adjustment and you have to be kind to yourself and acknowledge it's difficult without putting that on the kids.
I promise you though that long term it's a blessing. You get some time back to be entirely selfish which not many parents get. I tried to see it as, eventually you have to let them go and go to uni or move out or whatever and you have to find a way then to fill up your time that for so many years was taken up by school runs and lifts to clubs or friends houses and all that - you're just learning to let go a little bit a few years sooner. I'm not explaining it very well but it helped me to think of it in those terms. Something that had to be done eventually either way and I was just facing it sooner than I would otherwise have to.
I also kept in mind that no matter how much I hated exdp and no matter how much I hated the idea that whatever girlfriend he had at the time would be there, DS wasn't in any danger. Exdp doesn't meet my standards of parenting but DS doesn't come to any harm being there.
In the early days it was actually helpful. I got a day here and there to fall apart after keeping it together in front of DS.
I'm 6 years on and I can honestly hand on heart say that my life is SO much happier. I am chasing dreams I'd given up on (and achieving them). DS going to stay at his dad's is just my new normal now and I can even say I don't hate my ex any more. He'll never be my favourite person but we have vaguely friendly chats every now and again and I don't resent him for his actions back then, I can accept now that we just weren't suited.
And once you're the other side and you build up your life on your own to one you want, it gives you a new inner strength you never had before. I got together with my now DP a little over a year ago and I have no idea whether or not we'll be a forever thing or not but I very strongly know that either way I'll be absolutely fine and its so refreshing to be able to be in a relationship knowing that, it means you never accept less than you deserve.
This all sounds like some twee self help book extract but I just wanted to tell you that you will be absolutely fine and everything I've said is 100% true - you just have to get through this shit part first and then there's a much better life waiting for you so just remember that on your worst days 💐