I have the same problem, did you bleach your hair at all? My hair snapped off really short on most of my blonde streaks now. I have naturally dark brown-black hair since I'm asian, and I've been dyed my hair 10 times in the past year and 2 months. I've went brown with white blonde streaks to black with white blonde and red streaks, to black with ash blonde chunky streaks all over, then to black with brown streaks, then to brown, then to black and then back to light brown with blonde streaks. (Included in these were two times were my hair was stripped and 3 fills for the blonde areas)
Hairdressers have told me that it is snapping because of my constant bleaching and hair stripping since I had black in my hair, and then dying it back dark and then bleaching it again to get it blonde again. The hairdresser told me that I should use the Bed Head Dumb Blonde Shampoo and Conditioner and use Deep Conditioning Treatments once a week along with a Deep Protein Treatment once a week. For Conditioning/Protein Treatment I recommend Tiger Reconstructor, and for a Protein Reconstructor I recommend K-Pak's Deep Reconstructor. And I've been using K-Pak Daily Shampoo and Conditioner and they seem to work pretty good, except my hair doesn't feel moisturized enough. I use Bed Head Ego Boost for my leave in treatment. I've noticed a HUGE change in hair health since I last had it colored, although it's still not healthy. I think if you want a dramatic change in hair health, you'll have to stop chemically treating your hair all together until it grows out.