what would happen if I just stopped paying the mortgage and claimed I had to move out due to it being an unliveable atmosphere
Unless your lender is a charitable organisation with deep pockets and well-versed in domestic abuse, the likely outcome is that they will institute repossession proceedings if your h fails to pay the shortfall left by you stopping your payments and you could end up with a black mark on your credit rating. In other words, it ain't worth the risk.
While your name is on the mortgage you are obliged to make the agreed repayments of the loan, but pigs might fly it could be that he will agree to pay your share as well as his own provided he is fully recompensed for this outlay when the property is sold.
Without being in possession of all the facts/figures etc, no-one can fully advise you via the internet and I urge you to reach out to a domestic abuse advisor asap as you may have grounds to apply for an occupation order which would compel him to vacate the property while you and your dd remain in residence,
If you don't feel able to divulge details of your marriage to an advisor, I would suggest you make contact and ask for recommendations for solicitors in your area who have extensive experience of, or who specialise in, domestic abuse.
You don't have to live in a loveless marriage or with an abusive h. The help you need is just a phone call away - make the first step and give 'em a ring