I think it's great that have a strong emotional bond to your gfriend. This is lucky for her, as a lot of men are closed and distant.
I do have the same problem you have: feeling almost chemically dependent on the person I am with. I am just wondering if you have any abandonment in your past. I have been abandoned at birth and I have a physical feeling that takes over when I think the person I am with is looking at someone else, or I drive myself crazy thinking about a guy cheating on me... I also have this feeling with close friends. I need very exclusive relationships.
The best way I have found to deal with this is to actually tell people that I have abandonment issues, and that, therefore, I will sometimes act unreasonably, and that I need a lot of reinforcement.
So maybe you should talk about this to your gfriend, and ask her to show her love in ways that make you feel secure. Maybe you need her to call you when she is away, just to say: Hi and reassure you that she cares about you In exchange, you can do things that make her feel loved.
Romantic love is a crazy thing, and sometimes, it is emotionally so unsettling that it seems too much to bear. The world we live in is too fast and doesn t leave much emotional space to express true love. Most of us know more about the lack of love than the abundance of love, therefore our thinking is directed towards the lack and loss of love, and not the abundance and finding/ keeping of love. Little by little we can switch our attention towards the magic and healing of love and turn away from the fear. I applaude and admire anyone who has truly been able to achieve such a thing.