Of course you are going to be feeling awful, it’s really really hard right now, and sounds like you have had a really tough divorce which you must also still be reeling from. I have been there.
My ex and I have divorced 5 years ago and have 50/50 custody. I absolutely didn’t want to not see my kids and it was really difficult, and still can be hard not being with them day to day. I worried that ex wouldn’t be great having to manage them on his own in his time but actually he totally stepped up and has mostly been great with them.
I did some reading at the time and there’s research showing that, from all the kids with separated / divorced parents, those who spend time equally with both are better adjusted and do better in life than those who don’t. This is providing both homes are safe and loving. Kids are better off knowing both parents want to spend time with them equally rather than growing up believing one parent is less interested in seeing them. Didn’t make not seeing them less hard for me but helped to believe it was ultimately better for them.
Ex and I do however split the week rather than do a whole week with/ without them. it may be worth talking to your ex about this- a week is a long time for the kids to go without seeing either parent, as well as long for both of you to not see them.
To help me, I made sure I made lots of plans for my child free time- first nights my 2 best friends came round with lots of wine! I work full time so that helped and at weekends I made plans to go out in day / evening, visited free galleries, walks around town, staying with friends who live away and so on. Lots of times I did this on my own too. Kept busy. Also having some space, peace and time to get over the horribleness of the last year or so if the marriage and the divorce was helpful.
Once we had fallen into a routine and we had all got used to it, I actually realised not having the kids all the time can be a good thing for me too. I still miss them when they are not with me but I have a good life and so do they.
if yours are old enough to have phones then you can still have daily contact- I have a WhatsApp group with my two so we can message together as well as 1:1. If the kids need me they call and we can talk things through on the phone. Ex and I are relaxed enough with each other now that I can go over and see them in his time and sometimes we do stuff altogether.
Sorry, long post, but wanted to share to say that it can be ok, and you can get positives from a shit situation. Take a massive breath and make a plan for yourself- you will be ok x