Biologically designed for variety. You can repress it OR you can consciously do it and be honest with yourself and drop the guilt.
Since you have a long distance GF your need for intamicy, affection, sexual attraction will be high. No need to feel guilty about it, just the way circumstances are.
Like JSB said, it's simply appreciating beauty. If you get high enough in consciousness ALL women of any shape and form will be attractive to you. It will feel like sexual attraction but it's different, more of an appreciation.