Is there any reason why a girl would talk to an ex while she is dating?

before she blocked me she told me that she was dating someone now but then 2 months later she unblocked me because she thought I was lonely, I just don't get her, she unblocked me on 2 social media platforms just to talk to me, I sent her a friend request on Instagram and she hasn't even accept or reject it and it's just so annoying and when I text her nowadays she gets hot and cold with me and mostly leaves me on read

Is there any reason why a girl would talk to an ex while she is dating?
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