The best way to be less invested in a relationship is to invest in other relationships. The more time you spend with people who aren't your partner, the easier it will be for you to see them objectively. Honestly, the problem isn't being too invested. The problem is being invested poorly. The solution to that is not to be less committed; it's to be more committed — to something you have thought about carefully and decided is worth your time and effort and risk. That's what almost all of us need: something we're really committed to.