The Ex-Factor.

I want to know at what point in a relationship people change their inherent ability to be independent and suddenly NEED so much from another person.  In the absence of a significant other, everyone is just fine to live by themselves, to do their own thing, to rely on their family, friends, career... to live independently.  And then- they start dating someone.  And slowly they let that someone else into their world.  The stage of life that they are in usually determines just how fast the two worlds merge, but usually it happens at a slow rate.  Introductions to the family, meeting the best friends, spending lots of time at each other's home, eventually moving in together.  If its a relationship that is going to last, all these things happen- given time.   And slowly the two worlds become one.  The two groups of friends begin to hang out with each other, his friends become hers and vice versa.  The two families eventually socialize together.  And its one big happy family.  And then suddenly, neither the man nor woman is capable of existing independently anymore because they get so used to having someone else.  And they get so used to having someone else's world collapsed into their own.  I suppose that is why ending a relationship is quite so hard.  Its like two pieces of string all tied up in a million knots.  Before you can have two separate pieces of string again, you have to untangle each different knot and completely separate the two lives before the two can begin to live independently of each other again.  But does this mean that after ending a relationship with someone and finally getting your knots all untied and untangled that you can never be friends again?  I suppose its different for different people.  Different types of relationships etc.  But I think for me, its too hard to keep someone as one little connection in my life when they had been all wrapped up in it.