This is merely a starting point, but it seems to be a starting point for many of my philosophical discussions. For each and every one of us there is an inner and outer world - it is the interaction of these 2 aspects of our experience that determines the self.
If one takes language as an example: we all think in a language, and without it, we would find it extremely difficult, probably impossible, to conceptualise, compare, manipulate and develop abstract ideas. This is such an internal and fundamental process that we tend to forget that we all gained our language from our external world. My point is that we underestimate the dependence of the self on the external world.
This also extends to relationships, because without our interaction with others the self would be sterile, unreflective and probably unexamined. So the self is not something that we can consider in isolation of our external world because it has an extension into that world which both receives and transmits information, energy, emotion and our very soul.
What do I mean by soul? My own interpretation is that it is an evolving process, tempered and moulded by life that we can learn to be comfortable with or we can learn to inwardly dislike. The latter experience can create depression, hatred and a perverse outlook on the world. I speak from experience, so this is part of my journey.
For further elaboration on this, refer my post on The Meaning of Life.