Why does she call me bro?

Long story short me and my ex girlfriend are still in contact and sometimes she calls me bro even when we were dating but when we broke up we stopped talking for a while and she started contact after 3 weeks and went out a few times but she mostly calls me by my name but sometimes calls me bro and I've pulled the "sibling" card on her by calling her sis and she slapped me for that

So why does she still call me bro even though we aren't close anymore?

Why does she call me bro?
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