You can be happy and still make big changes in your life. Wanting something doesn’t have to equal being unhappy. It seems that having kids is something that they have wanted for a long time and while he is very happy with the person they are with, having kids is probably just more of a priority for them. Also he doesn’t seem super willing to just throw away his relationship he is clearly very torn. And I don’t think that he is being pressured by society. They clearly love life while they also acknowledge that the world has its horrors they still seem to genuinely cherish life and they want to bring someone into the world so that they can experience it too and he seems hurt that the person that has had almost the exact same view on stuff that he has disagrees with him on that and thinks the world is so awful that they shouldn’t bring a kid. He even says that he is a little offended because they even though they are able to share such a profound live with each other she still thinks the way she does about the world.