selling house & going to an apartment...

Keep the house if you can!
Renting builds no equity and as a woman we don't often have the same pensions etc and you can't rely on a man! And apartments for single mamas can be depressing (especially with laundromats, noisy neighbours, and other interesting things that happen when you live around other people)

Draw up a budget with your expected financial support from ex partner.

If you can't live in it what about keeping it and renting it out while you find a new place a bit cheaper (could even buy smaller home?)

But get all your financial ducks in a row then go talk to financial advisor/banker/accountant friend that you trust...

I'd try to keep the house. Look into what an apartment would cost, you might be surprised. In our area a small 2 bedroom with no bells and whistles costs as much as the mortgage on our 2300 and 1/2 acre.

If you've owned the house for a few years look into refinancing and lowering your payment.

Yeah... and if you can't refinance and you've been there at least 5 years, ask them to "recast" the loan. That means they take the remaining balance and re-amortize it for another 30 years. It extends out the life of your loan, but can lower the balance without the need to go through refinancing.

I would try to keep the house, too. You'll never save enough to match market appreciation of a home.