I'm so sorry about your recent development. Confirmation of ow is a devastating thing, even if it was already suspected. I've been exactly there.
I won't offer advice on your R. I'm new to this, myself. (I can't believe I'm still saying new, because it feels like decades already).
So, I'm no vet, but a couple of things they repeat here often that have helped me, are the good-old GAL and detach. I'm learning to really focus on improving my self-esteem, and make sure I'm taking care of my kids. That has been worth gold.
It seems you are already making good progress in that department, especially since you went on a cruise! I'm glad you were able to do that for YOU.
So, this MLC stuff is a long, drawn out rollercoaster ride, and anything can happen. And it often does. Don't beat yourself up if you feel like you're sliding back or have a bad day. Come here and vent like the rest of us.
As far as disclosing things to the kids, I agree with you, to not tell them anything about ow. Your kiddos are quite young, and they have many years to deal with this ahead of them.
Honesty is always important with regards to the kids. Lying and pretending everything is ok doesn't work. I believe they see through our attempts to hide things. But, it's a fine line, right? Balance with minimum info, and speak in generalities, no details. Constantly remind them you are there for them, and that no matter what, they will be ok.
I would NOT, however, speak negatively about 'dad' to the kids. Whatever it takes, hold it in. All of it. Your opinions, logistics of his job, his choices, what he could or couldn't be doing....none of that is good for the kids, either now, or down the road. This is one area I do know well.
Even saying "daddy could get a job here"...true as it may be, all they know is "daddy isn't choosing to be here with me." Probably not the best thing to put the words out there. That's a tricky thing that could come back on them later.... Just my .02.
Hang in there, fthnluv. You have already dealt with so much, and you're impressing the socks off me with your calm. At least you write calm. . (Behind the scenes tantrums are also acceptable).