It's your BPD all the way. It's called splitting sometimes when we go from one extreme to another. It's stereotypical, but for many BPDs they fall in love fast and are totally infatuated with a person and then they start seeing their faults and go from love to despise very fast. Not always true but sometimes.

I think the reason BPDs fall in love so fast is because we lack the validation that love brings. We were told we were unlovable, despised, forgetable, so when someone shows us attention we latch on, cling on much more than we should.