My Dh's first wife had severe fertility issues. He said he was ambivalent, neither for or against, but she wanted to try, so they had a few failed IVF attempts. They divorced shortly after for many reasons, mostly that he wanted to relocate overseas and she didn't.
Fast forward 20 years, ( now in his 50s)he is a step dad to my three, since 2021. He says that living with the kids has been ultimately, one of the most surprising and fulfilling parts of his life. He is involved, knows/ makes them a priority and takes the relationships seriously. There have been bumps with the integration, of course, but there has always been an honest dialogue that is solution driven.
He left his last long term GF as she wanted kids and he thought that he didn't want to change his lifestyle. I know that she finds his new step dad persona hard. And I understand why. The options were that he lied to her about not wanting kids and/or didn't love her enough. It is a hard pill to swallow and I would feel the same as her.
Men self prioritise, if they don't want to do something, they won't do it for someone else. Only if they want to, for themselves.