Crystal clear about not wanting kids

I (36F) have been in 3 long-term relationships (12 years with my high school sweetheart, 3 years, and 4 years long) and in all of them, I have never, ever changed my mind about wanting children, and as I’ve gotten older, I’ve continued to make it very clear with my partners that I am not interested in having kids or taking someone else’s kids on. My partners have always said they’re good with it or are also not interested in having kids.

Yet, every time a long-term relationship has ended, the reason they say it’s ending is because they’re having second thoughts about having kids. (Luckily, I have never been married so didn’t have to go through divorces over this topic.) I just had a month-long fling with a potential new partner, and he ended it this morning (via text message) with the same thing.

I truly understand that people can change their minds about having kids, but … my god, what can I do? I’ve considered getting my tubes tied to be done with it once and for all; sometimes I think my partners don’t take me seriously or that I will change my mind.

This may just be a vent session but want to know if others have experienced this over and over again? It’s getting discouraging, and I’m starting to get paranoid about future relationships where this concern will forever live in the back of my mind. (It’s obviously a topic my therapist is quite familiar with, as well.)

Appreciate any personal experiences or advice - thanks!