Hello Alyson and welcome to the site.

"Not really a poem" - well, sometimes, these are the best poems. Unpolished 'rants' that come from the heart and move people immensely; after all, what is poetry if not that?
I don't know who this person is (it could be a sister or a friend) but they mean enough to you to rouse such strong emotions.
You are absolutely right when you say children should mean everything to you. When you have them, there is no 'time out' (for any length anyway) and no coming and going as you please.
I am very sorry to read that you can't bear children - but it sounds like you have had an important influence on these three little lives when you didn't strictly have to. If only all parents treated their children with that kind of love. Being a parent doesn't necessarily make you a real parent....there's a good deal more to it than that.

All the very best and stay well,
Ben

@ double post