The Short Version
The claim conflates early-stage passionate intensity — which research does show fading within roughly 1–3 years — with romantic love broadly. Multiple high-authority sources, including the American Psychological Association and Harvard Medical School, explicitly distinguish these constructs. Neuroimaging studies show couples married over 20 years can exhibit the same dopamine-rich romantic brain activity as newly in-love individuals. The blanket assertion that romantic love "typically lasts no more than three years in most relationships" is not supported by the preponderance of scientific evidence.