Sometimes, despite your best efforts, color-treated hair can become brittle, which makes it more prone to breakage and more likely to fade faster. You can avoid this fate by switching your hair products to richer formulas and scaling back on your routine.
Colorist Marie Robinson told Allure magazine, "If your hair breaks easily, it's probably either very fine or has been overly bleached and lost its elasticity. Hair color always fades eventually, but it will fade more quickly when hair is damaged. To keep it from becoming more porous and brittle, avoid bleach, shampoo infrequently, and only get highlights every eight weeks. Try not to heat-style more than a few times a week, and always use a protective product."
Allure also suggests drinking plenty of water and taking a biotin supplement, which can help your hair retain its moisture. It may take a while to see results, but in the long run it'll be worth it.