Why does my friend get kind of aggressive if I don’t reply right away or respond how she wants?

I’ve always been pretty responsive. However I started a new job and it’s been busy and I am not by my phone a lot. Anyway she’ll blow up my phone if I don’t reply or text me something like “K” if I just heart one of her messages.

Why does my friend get kind of aggressive if I don’t reply right away or respond how she wants?
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