Stop putting yourself down. Now. This is the last time you're hard on yourself.
You've made a huge leap forward in articulating to us, and more importantly to yourself just what is wrong in this relationship.
And not one of those things is you.
You're the woman who's created a family, kept out of debt, made a home.
Bailiffs at your door?! Because of his tart debt???
Can you rally close family and friends first and open up to them?
Prepare a clear, calm statement, setting out what exactly he has been doing.
The effect every aspect of his behaviour has on you.
And how anxious you are about what that will in turn do to your children.
(You've had good practice right here; start with your posts to us and refine them).
Then say for those reasons I've made my final decision to cancel the wedding.
At this point you'll discover who your real friends are!
Acknowledge and apologise for disappointment, costs they may have incurred.
Luckily it's a rented place - time to create a home for yourself and your children.
You may need someone with you when you tell him.
I do hope you'll find the courage - we support you.