J.J.
Oh J. -- I've been where you are. I just hope you will thoughtfully consider carefully what you are doing better than I did. Things before we married were a "little difficult" probably like what you are going thru. The ex got 100 times meaner, demanding and after every cent we made. We went in and out of court time after time. A good, loving, caring man giving his kids everything he could. She was completely out to ruin us financially and our marriage. She got the kids against us and it became all-out war. Face it girl, the kids are going to think and believe whatever she pumps into their heads - she is their mom and if she has custody she has a lot more time to fill their heads. In our case, everything that went wrong in the kids lives was turned by her to be our fault. It made my life MISERABLE. I tried, I loved, I cooked, bought goodies, made treats and I was the villian no matter what I did. They are adults now and hate me anyway. There is a wall up that I fear will never come down.
Just for your own sake - WAIT!!! You are only 25. Give it a year and decide if things get harder (I promise you they will!) do you want to have that in your life? I am sure he is a great guy (mine is) - but do you want this struggle and lack of peace to be what your life is about? It took away a lot of happiness in my life. I am peace loving and want to get along with everyone and it made me miserable.
The kids are grown and our lives are a lot better without her having a legal hold on our finances making obsurd and unreasonable demands, which makes it a lot better, but there is still no loving and united family.
Think it thru carefully and decide if you are willing to take this on for years and years. Those kids are young. You will have until they are 23 if they go to college (and you guys will get to foot most of the bill if they do!!) Believe me, after she gets him for more than he can afford, you will be working just to make ends meet in your house. You will eat peanut butter and jelly and watch network tv while they have $200 tennis shoes, leather jackets and full-selection cable tv.... screaming how much they hate you!! Just my experience... give it serious thought!!!