If he will drift away and not see them for weeks on end then he's a shit dad and that will leave them with more issues than having a safe and secure home with you where they know they are loved, wanted and valued. Better they have a full life he drifts from than a halfway life he is already drifted from surely.
I've been the kid when parents say "we stayed together for you" and I felt pissed off and guilty in equal measure.
They weren't happy together. I learned a blueprint of "normal" relationships which was actually totally unhealthy and has taken me years to unravel.
Really my parents didn't want to deal with the consequences of a break up because it felt such a big step for them and they considered it "giving up".
In reality they just kept us all in a tense, mediocre, awkward limbo for years. And for nobody's benefit. Then split up as soon as we were adults, with an affair from one of them thrown in for good measure.
You're going to teach your kids that unhealthy, cold, distant relationships are normal. And that its normal and OK for parents to be a bit meh about their children.
You're obviously very bright. It sounds like you're making your decision based massively on what other people with think and the inconvenience it will cause, rather than what is genuinely best for your kids.
I hope I'm wrong but from the outside it sounds like that. It must be tough but you're bright, capable and in a fantastic position financially.
What happens next is up to you, he has no reason to make a decision if you aren't either.