RE: all the people saying the man should pay more in this conversation, let's discuss a hypothetical situation:

A husband and wife enjoy walking through the park every evening. One day, the wife suggests they walk a different way home. The husband agrees. On the way home they pass a petshop and see a snake in the window. The husband gushes about how cool the snake is. The woman just says "Meh." They both enjoy walking this new way home. The next day the husband suggests they again take the way past the petshop, and the wife agrees. The next day, the wife suggest they again take that way, and the husband agrees.

The next day the husband decides to go into the pet shop and pet the snake. When they get home the husband pulls a snake egg out of his pocket. The woman is angry. She did not want a snake, she does not like them. The husband says it was an accident, the shopkeeper did not speak English very well and when he said he wanted to pet the snake, the shopkeeper thought he wanted a snake egg.

They attempt to return the egg to the petshop but find that the shop is closing down and all eggs that are not given away will be destroyed. The husband refuses to return the egg, as he does not want to "kill the baby snake." He also refuses to give the egg to someone else as he has become attached to it. He thinks to himself, "My wife will come around when the egg hatches and she sees the snake. She will grow to love it too." The man and woman take turns caring for the egg and when it hatches, the snake, but the woman never grows to love the snake.

Later, the husband and wife get divorced. The man leaves and takes the snake. Since the woman agrees it was her fault for taking the man past the petshop in the first place and agreeing to go again, she agrees to pay half for the snake's food and vet bills for the next 10 years. The basic food and water costs $20 a week, and the snake does not go to the vet every week, so she gives the man $15 a week.

But the man wants the more expensive food that costs $50 a week. It makes no difference to the snake, the cheaper food is just as healthy. He buys it. He gets a new girlfriend that loves snakes. She helps the man buy expensive snake-clothes and a new fancy room-sized tank with a waterfall. The snake would not be unhealthy in an average sized tank without a waterfall, but these things look nice. To buy these things cost $5,000 and to keep this tank heated and run the waterfall costs $100 a week. The man and his new girlfriend buy the snake $20 worth of snake-toys every week. They buy expensive pet-health-insurance for $50 a week. So they are spending a total of $220 per week on the snake, and occasionally spend more, and the ex-wife is contributing $15.

So the man thinks, since he is spending all this money on the snake his ex-wife helped him acquire, his ex-wife should pay more than $15 a week. He says this to the ex-wife. The ex-wife says "No fucking way. I never wanted a snake. I am paying for half of the snake's needs." The man says, "How can you be so callous?! This is your snake too. Don't you want him to have this great life he has become accustomed to?! How can you expect him to just rot in an average sized cage with no waterfall? How can you expect him to not wear pretty clothes and play with nice toys?"

Who is in the right here? And before anyone says "But a snake is not a human! I love my child more than I ever would a snake!" - That is the point. I am asking you to think about this situation with logic, not with emotion.