The Happy Together Tour arrives at the Westbury Music Fair as a live rock/pop bill built around a shared era rather than a single headliner. It draws on the lineage of mid-century radio pop and harmonized rock, presented as a moving snapshot of how those songs still circulate in American memory. In the New York region, this kind of packaged nostalgia has long functioned as a recurring concert tradition, linking suburban venues to the city’s music economy. The format can flatten differences between artists, but it also makes the lineage easy to hear.