Are you scared your partner will change their mind?

I'm firmly childfree. We've been together for nearly 10 years now, and we're still in that "fertile age" so people bother us sometimes with that. But most of our immediate surroundings are accepting, which is great!

BUT

I have this lingering thought that maybe he will change his mind and leave me for a woman who wants kids. It's like my irrational fear. Anyone else has this fear? What can I do about it? Every few months I let him know this fear comes back... and he says he still doesn't want any kids, and we're good and happy living this way. I'm scared to lose what we have built. A child would ruin everything...

Anyway I'd love to discuss with you guys! Thanks In advance!