how do you overcome sadness?

Sometimes I find myself incredibly disconnected,
like I was here for the wrong reason at the wrong time...
I’m sad,
& I don’t know how long I’m going to be like this.
But I think as long as I cling to the things that I miss,
I would be like this for the long period of time...
how do you overcome sadness?
Am I that strong to let go of the things
that make me sad knowing that
it’s the same thing that makes me happy?