Why do we love Or fall in love knowing full well that we will lose each other in the future?

We love people around us, get attached to them, find friends, love, and family.
I mean family is kind of something we are stuck with loving or at least have some attachment to but why others?
We all know in the end we will lose them or they will lose us, it is inevitable but still we get attached. I won't say I don't get attached cause I do and i try not to but still it happens, I just don't understand why?
Why do we love Or fall in love knowing full well that we will lose each other in the future?
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