How to deal with a breakup?

A few hours ago my (now ex-gf) came back from her holidays and broke up with me.
She confessed me she had cheated on me while she was away.
Now I feel like... totally empty and broken.
I didn’t even get angry with her, I just said “if that’s how you feel I understand you” while she was crying.
Now I can’t sleep, and don’t know what to do, I feel like shit.
How to deal with this feeling?
How to deal with a breakup?
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