I'm so sorry, Katie.
It is a common ploy with active addicts to take cheques from the middle of cheque books and use them...they are not noticed for quite some time, long after they have used them. If you check your cheque books I'll bet you will find some missing from the middle...or a book of cheques if you have an order of new cheques.
Charging him, working with you bank and holding him accountable is the only way to protect yourself from him.
Sadly, I know all this because my own son did the same thing.
We learn and then we learn some more. Hope you can manage with your mortgage...perhaps call whoever holds the mortgage and tell them what happened and that you have reported it to the police. Many mortgages have a clause that allows you to miss a payment once or twice, without penalty.
Keeping you in my prayers.
Hugs