Well I find it interesting that you consider her a perfect match and you want her to yourself to build some kind of life with yet the two of you conflict on a pretty serious issue - She clearly seems to want kids. You don't.
That said, like the above person - Why do your deep feelings translate to exclusivity for you? Just make your feelings known. Make your intent, desires, and all your aspirations for your relationship known.
If the feelings are returned and mutually supported then you should have nothing to fear. They're already inviting you to move with them, so you seem to be an important part of their (her) life. If your feelings are returned... I'm not really sure what more you'd want.
But really, if the woman truly wants a child, that's something you're going to have to come to terms with regardless of the scenario.