I can share a different, but sad perspective on this.

My MIL has has an partner (at 70 is it really a BF ) who sadly lost his only son in a car crash when he was 19. His wife didn't want anymore children. He told me she did express regret that she didn't have another child but it was too late to do anything about it by then.

Now he is a part of our life as MIL's partner (his wife passed a couple of years ago) and he told me that while he is loving it he is also sad too that he has no grandchildren of "his own".