Is the father meeting half or even a quarter of the costs of bringing up his child? (This includes housing/ utility/ food/ school-related/ extra-curricular activity costs, not just the child's clothes/shoes/uniform and personal items).
Is the father doing half, or even a quarter, of the childcare time?
Is the father doing half, or even a quarter, of the school runs/travel to clubs and activities/ ferrying about to friends ?
Is the father doing half, or even a quarter, of the parents evenings, help with homework, school-related admin such as applications, replying to letters etc?
Is the father doing half, or even a quarter, of the cooking, cleaning and laundry for his child?
Is the father doing half, or even a quarter, of the dental appointments, doctors appointments, vaccinations, time off work when sick, or haircuts for his child?
I'm guessing that he probably doesn't. Yet he's complaining that the one burden he has, once a month, isn't shared equally by the mother, when he was the one that chose to move away?