Mia, Please go see a lawyer and/or solicitor as soon as possible. You need some protection and yes money to help out w/the mortgage. Just because his name is on the mortgage, that doesn't mean he will pay it even if it's stipulated in legal documents. Some of these people will allow their homes to go into foreclosure rather than pay.
Protect yourself and your children no matter what. This is a business transaction that needs to be taken care of asap. Taking him to court may not tip the scale one way or another as to whether returns or not.
Please protect yourself!
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.