How can I get over my ex

I've tried get over my ex many times, but I've not be able to do it yet.
I cannot help thinking is there any way to get back together.
Every time I get a message from her, I cannot help be happy.
Every time her reply are very simple I feel sad.
I don't think she continue to love me.
How can I live without her.
The answer seems not difficult, but it's difficult for me.