Blood Relationships (with increased clarity)

There are people who come into ur life at particular instances! (Like sometime during school,
college, work, etc.. ) But this meeting you will cherishwhile it is happening. You will wish and think will last life long.
And they may be some which are ur blood Relationships. For eg: ur parents, sisters, brothers, their relatives, other relatives, etc. These ppl you would have spent time in patches, some regular intervals of your life. During these moments there may be instances of wonderful time spending and instances of hurt, disappointment, etc.
If there are hurtful disappointing experiences amongst friends, you may choose to abandon them. But it is not so when it happens within Family, Blood Relationships and almost Blood Relationships. Why is that so?
When you find the Freinds taking a different life path from urs, you dont mind losing them. However, if your Blood Relationships take a different life path, you do mind. You still feel you belong to them. And there is this invisible umblical cord connecting both of you. You make all the effort to stay in touch with them. Watever happens in your life: eg: you insult them, they insult you, you cheat them, you create a mistrust, they act calculative, you find either of you swinging back into a good relationship.

Why?