I've also heard you mention--on several occassions--that it's "too easy."Yes, she's very much into me - but as a person - i'd like to have someone who challenges my mind.
I still think this is the key "what's missing" in your situation. Ultimately, a fulfilling long-term relationship keeps both people wanting to RAISE THE LEVELS.
And by raising the levels, I'm indeed referring to challenge.
To me, challenge doesn't just have to be "gee, she doesn't call me enough--I wonder what she's up to? Boy, I'm sure interested now!"
It can also be, "whoa, this girl has a totally different opinion of (a song.) I hadn't thought of it THAT way..."
I think of it kind of like this: It's important to want to feel motivated to "one-up" each other, because that keeps things interesting--like you just want to impress one another. However, the minute one person feels like they're in total control of the relationship, they get bored. Game over--challenge met. Instead of two independent people enjoying each other's interests and opinions, it becomes ONE person enjoying THE OTHER PERSON'S interests and opinions.
Perhaps that's your situation--this girl, great as she is, just isn't someone you have a deep, satisfying, stimulating MENTAL connection with.
It's happened to me before.