There is no fairness in divorce and it would be impossible for anyone here to answer that one.
I replied to another poster earlier who was also married for 3 1/2 years and I stated there that it would be seen as a short marriage and that as there were no children involved each party would take out what they had before marriage. Your case is different as there are children involved and you will have a responsibilty there by law. This bit you probably know as you are already have CSA information.
I also think you need to post a bit more information about the family home regarding equity and other assets you might have.
Hopefully the more knowledgable here can point you in the right direction.