Alright, come on. This looks like it's about to turn into a flame war, which, no I'm not minimodding or anything, it's just no one likes that shit.
1.) Yes, the bare core of relationships is reproduction. It's reproduction because sex is what is used for reproduction, and as a failsafe to prevent people from just "Never doing it" the human body has a built in desire for it on some level at all times.
Sometimes it's only to the degree of "man a hug would be nice" or something like that, but yes, the desire for sex, and therefore the failsafe for reproduction, is the cause of relationships. Thus why, you know, they are usually aligned with someone's sexual interests? :/ /instaproof
Anyway, tell her. I've been through enough shit to know that not telling her will suck a lot more than a "Oh, well that's really sweet, but...".
Because any reaction is better than wondering what the reaction would be.
EDIT: Goddamn page 4...