Hey there
Nope not sure regarding the label thing. I can relate to what you say regarding intense feelings being superseded by indifference. I think it's either that you are in need of a person of whom you feel understood and whom you can have strong feelings to, but your girlfriend isn't really that person and instead you so to say try to shoehorn her into that meaningful, understanding person she really isn't and are therefore all to willing to interpret rather meaningless conversations with her to be much deeper.
Or maybe it's the other way round. Maybe you actually have strong feelings for her, but there's something in you that needs to distance itself and shut down warm feelings. That could be a sign of an avoidant attachment style. There are two kinds of avoidant attachment style, one being anxious-avoidant, the other one dismissive-avoidant. Maybe you want to look up this terms for you.
That's all I can think of at the moment. Hope it was of some benfit for you.