Why is my ex boyfriend giving me sad looks?

We literally haven't talked all month. And I'm pretty heartbroken over it, he just decided one day we won't ever talk again I guess. But today at lunch I was laughing with my friends and having a good time and he kept looking at me, but his facial expression was like sad? I'm just curious to know, I never broke his heart, he wanted me to break up with him beginning of November.
Why is my ex boyfriend giving me sad looks?
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