Oh dear, you really have been put through the ringer!

Your DH sounds like an immature brat! Sounds to me like he just wants to be able to come and go as he pleases without any consequence. You need to decide whether you want to work on your relationship or not, if you don't want the marriage to continue don't let him come back again...if you do want to work on it, then he comes back and doesn't leave again (unless it's permanent)...don't let your home become a revolving door for him to use as the mood takes him.
My DH and I are no stranger to drama, lol, he has threatened to leave many a time...but he hasn't yet...he knows once that door is closed behind him, it doesn't open again! I have told him time after time if he wants to leave that's absolutely fine with me, just make sure you are 100% certain, cos you won't be coming back, LOL. Same goes for me...I have wanted to give up and leave as well, but I know once I leave, that's it, it's over, I won't be coming back!
Use this time without him around to think about what you really want for and your children. Don't be scared to "go it alone", you CAN do it! Sometimes I think the only reason I am still here, is because I'm too scared to leave.