Your argument contradicts itself. We're individuals, yes, so how would you propose that we avoid self-involvement? We experience the world through ourselves. Life can't REALLY be experienced any other way. That empathy we feel for others? How we think we understand them? It's us relating events they've experienced to our experiences - self-involvement. We can't ever really understand another human being and what they experience. To think so is perhaps one of the biggest mistakes humanity as a race makes. Though we like to think of life a universal constant, it's different for everyone. Our relationships are connections, ways of establishing links to other individuals, to feel intimacy. And these feelings really do make us percieve another person as a part of ourselves. So yes, letting someone go is a physical experience. We cry. We hit things. We yell, we scream. We feel as if parts of us are being torn out, and we expel those part of ourselves that another person made up. It's how we reconcile ourselves to their absence from us. That is how much our relationships mean to us. Without them, we'd be alone. With them, we don't have to feel alone. Which is really what we are in the end. Alone.