screwtape, i dunno if you will ever read this, but here is my 2 cents on the librarian:
I would still say that the approach you last advocated is not the best choice, because you already asked her out and she said she had a boyfriend. As a woman to whom this has happened, if you said you "cared" about me the 2nd time, still barely knowing me, I'd think you wanted an "in" romantically. Even though this might be what you want, you still have to be friends with her while she's dating this guy, and get to know her. (maybe you won't even like her romantically once you do this! happens all the time.) I'd advocate much lighter language. And spoken, not written. Something like, "hey, I know you have a boyfriend and I respect that, but I think we might hit it off as friends so I'd like to get to know you on those terms." that will let her know she is a cool person in your eyes, which is I think what you want to do, without making her wary (and she also wouldn't want to make her boyfriend suspicious if you were still indicating romantic interest, so she'd probably not want to see you in that case). and then you get to maybe make a new friend.
good luck