My best friend got married about 4 years ago. Before they got married they discussed having kids and decided to wait a few years and then go on to have 2 kids. About 2 years ago he suddenly came to her and said he'd decided he never wants to have kids, he'd never change his mind, and he'd understand if she wanted to get a divorce because of his decision.
She was devastated. He'd never let on that he was second guessing their decision to have kids and she's always wanted them. She's a very religious person and takes her wedding vows very seriously and won't consider divorce. She's miserable about it though. She keeps herself very busy with other activities and a second job, but has confessed she only does it all to keep her mind off of not being able to have kids.
They've gone to counseling over this, with no real solution and their relationship has definitely suffered because of this divide. I'm not sure they could be happy together forever if they have differing opinions on this huge life issue.
If your SO suddenly decided he didn't want to have kids would you consider divorce? I think that if my husband had done a sudden 180 on this issue that I would have considered divorce. It sounds so bad, but I think I would always resent him for taking that away from me.