You know he is leaving for a year and it is increasing your frustrations with the way things are at this moment.
This moment does not define you or your life. It should not be allowed to either. This is something you need to meditate on.
Do not let your fears of his leaving you with the kids taint your life with the kids. It is completely normal to know you will need an occasional break from the kids. If he were not leaving you could expect that.
Since we know that is not the case, you MUST start considering how you will begin arranging some quality time for yourself. You must start planning who will help you make this happen. You must start looking at full week camps for summer breaks. Send the kids to one camp while you go to another. Have someone responsible on call in case one of the rug rats breaks an arm and you can't get there for a couple days.
Who can take them for a weekend every couple months? Who can you trade out with? Surely you can watch someone elses kids on an occasional weekend if you know you are going to be treated in kind.
If none of that sounds possible, buy a few dog costumes in kids sizes and find a local kennel run by a very near sighted OLD person.
You must start taking care of yourself on the next level.