Thank you all for the support and advice. I called CSA yesterday and the lady basically told me what you all said. She also said that the way they look at it, if we were still together then DS would be benefiting from 100% of both our incomes. So the estimate is pretty reasonable considering.

Now I just need to get the guts up to call XP and tell him that I won't be doing a private agreement, and even if I did it would have to be similar to the estimate as I would want it to be collected by CSA (I don't trust him to pay it himself since last months payment was delayed twice and not even paid (AH! $38 not paid, and he's earning that much.. ), but at least I can keep a record of these things through CSAonline, I won't tell him I don't trust him though).

I forgot to add, Zennie, yep, I am getting PES & JETCCFA, which is helping out a lot, especially at the start of the semester when I need to buy text books! If I didn't have JET I wouldn't be able to study at all, and I so want to hopefully make a better life for me & DS rather than me going back to a job in retail. I know I won't be earning heaps in what I'm studying for, but I also want to hopefully show DS that you can have a job you enjoy, unlike what I felt about working at a supermarket heh