Is this fair if I give her $400 a month, provide healthcare of $188 a month, food, clothing, and diapers etc. during my 28.57 % of the time?

I came home with $28,000 last year. I have two year old twin sons that I take two days a week (28.57 %). We were never been married and she pays a total of $750 a month in child care of which the boys do not attend during my time with them because it's not needed. In addition, she obviously provides food, diapers, and other needed items during her time with them. I also have a small business but I have taken 0% profits from during the 2015 year.