Poe doesn't blame Rey for being cautious when it comes to relationships. How can he, knowing what he does about her history? Most people wouldn't have survived her circumstances, so for her to make it through at all is extraordinary. Let alone to flourish, take down a tyrant, and seize the future with both hands. Opening herself up to caring for Kylo Ren, only for him to die before her feelings could be fully explored, made it even harder for her. But he can't accept that the answer is for her to close herself off from all but the shallowest of friendships.
Still, even though he knows it's the last thing she'd want, he can't help but grieve for what she's lost along the way. As someone who grew up with two loving parents, surrounded by warmth and security and guidance, he knows how vital and transformative it is. Rey may have flourished in spite of her environment, but he wouldn't be half the man he is today without his. If he ever marries, he wants – expects – his household to be built on the same principles, and if he ever has children, he's determined that they will never know any different.
Not only has she missed out on that constancy and support as a child, but by shutting herself off now, she risks a lifetime of never knowing the strength that comes from loving and being loved.
Poe has no doubt that Rey's strong enough to succeed either way. She may even find happiness in the small moments along the way. But he knows how much more there is out there, and he wants that for her almost as much as he wants it for himself.
It's too soon after her loss to push the topic. Given how stubborn she is, doing so would only isolate her further. But one day, when she's ready, he'll make the case for being vulnerable.
He can only hope she'll be willing to listen.
A/N: Prompt: 'I know that a life without love is no life at all.' from Ever After