the actual moral of 500 Days of Summer:you shouldn't use the fact that you think you're a nice guy as an excuse to project your fantasies onto women who don't return your feelings. If she says she doesn't want a relationship, then listen and accept this.
what most dudes take from 500 Days of Summer:any woman who doesn't want to date me is a bitch. It's a fact; they even made a movie about it.