S/o never wants to watch our son

We have a 4 month old and I'm pregnant again, he only has to watch our son on his days off, he throws a fit and I watch him 5 days a week and have put off school and a job for my son, can someone please put me in his mind I just don't see why he can't watch the baby , he has 8 siblings and it's not like he hasn't had experience with babies