How do you help a toddler through parental separation?

Poor little thing, how sad.
There is no doubt he'll suffer but if you see him regularly, just try to be as loving and undemanding as possible.

Being two is difficult enough but being 2 and losing your Daddy will be awful. How often will he see Dad? You seem to imply half the week, is that right?

A few things you might consider: don't worry about regression, he may want to be babied a bit more.
He may not sleep too well and become fearful.
He may also become more demanding.

Never say anything bad about Mum not even when you think he can't hear you - children have ears on stalks, even when asleep!.

Allow for the fact he may be scared about losing you as well, as you are associated with the Dad he's losing in some way.

If he can stay with you during the house move, that would help, then he doesn't have to see all the upheaval.

Try to make his 'lovely new home' sound exciting and nice but be aware he'll actually want the old familiar.

Be consistent with routine when he's with you. He will need some stability.

Just love him and show him lots of affection. You can't do much more.