My Ex gave me her new number?

We hadn't had any contact for a few months except one time when we ran into each other unexpectedly. She seemed uncomfortable and we kept things short. She's also with someone else now so it's safe to say she's over me and I wouldn't say we're friends. But I got a text from a new number late one night and it turned out to be her. So now I'm confused, why keep in touch?
My Ex gave me her new number?
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