The Power of the Space Bar

There's a small difference between a girl friend and a girlfriend. That small space, silent to the ear, speaks volumes on how one should react to and interact with this person. It's apparent to some people on which one is being used, knowing the context of the sentence, and the people involved, but other times, it's not so clear.

This lead me to think: what does this space actually signify? After much thinking, I didn't get anywhere, as it was a question too simple to over-think, yet too complex to provide a simple solution. While busying myself with reading, a relatively satisfactory solution appeared in front of me. The space is like a termination of a thought process. It is how we denote that a bundle of letters jumbled together creates one coherent thought/meaning, and is then separated from the bundles of letters before and after it.

It's a thin [invisible] line separating those two ways of addressing someone; isn't it the point to find a boyfriend/girlfriend who has those traits that allows you two to be best of friends? What dictates the differences? Why are there differences? What changes when that small space is deleted?

After all, shouldn't it be nothing?