Why is she still contacting me after all that's happend?

A brief summary. I fell in love with my best friend.At least I thought I did.I thought she felt the same about me,but has since caused me stress,taking her feelings back, but yet comtinued to hang out, flirt,share a bed on many occasions, etc.We never officially dated,but spent maybe like 5 days a week hanging out, etc.We've spent the past month or so bickering.It starts out me asking for time apart to get over her, her not understanding why I need this time,continuing to mess with my mind,then eventually telling me I need to get over it and that she'll leave me alone from now on,then eventually she'll send me a text asking how I'm doing and eventually giving in.Well, this last time was a doozy.She's even dating someone new.Luckily for me, I've met someone new too who happens to be incredible,but it's still in the beginning stages,but so far so good.Anyways,I get another text from my ex-best friend, wanting to drop off stuff,and give me a birthday gift.I thought I was going to be