<human>: I've never really dated before, which is why I've come here.

Basically, there's a childhood friend that I once had a terrible 'date' with, basically the textbook example of inexperience/things going wrong. Not calling it a 'date', awkward hugs at the end, the works.

Anyway, I thought that ship had sailed, but come a week or so ago, she called me up and mentioned that she wanted to give me a second chance. 

So we went on a second date(officially a date this time) and she mentioned that she wants to be more serious and is looking for a long-term relationship. We ended up talking for about 7 hours.

And after a nights sleep, I came to the conclusion that she's a good friend, but not someone I'm interested in romantically. However, she's going away for several weeks, so I wont see her in person for a fair while.

So my question is this; how do I tell her this? Should I send her a message on facebook immediately? I probably won't see her for several weeks at least, and I don't want her making any assumptions during the interim. Should I wait a few days and then send her a message? Wait until we see one another again?

Any advice appreciated.

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: Girl looking for long-term relationship, I see her as a friend, wont see her for a while, want to let her down easy.