I'm curious as to how you know you could be BFFs with this person if you haven't interacted with them much OOC? RP, especially good RP, can create a false sense of closeness, but unless you chat or plurk or email OOC, that closeness is purely about good CR and good writing. It's awesome that you're having fun, but try to keep that perspective - and in the meantime ask the person if they're interested in getting to know YOU rather than just you're character. The worst they can do is say no, which will suck, yes, but at least you're not left wondering what might have been.