Just so you know, it's the Blue Hills Bank Pavilion.
Which hotels did you try? What are your dates? Budget? Any hotel in downtown can be convenient to the pavilion either by public transit or Uber/Lyft.
Others in the immediate area - Westin Boston Waterfront; Envoy Hotel, Aloft Hotel and Element Hotel. Assume you have looked at the Seaport Hotel and the Renaissance Boston Waterfront since they are closest to the Pavilion.
Boston is very small and you don't need to stay in the Seaport because you're going to concert, unless you ant to. IMHO the Seaport area is a soulless collection of convention hotels and office buildings with a whole lot of expense account restaurants. .I suggest you stay near the Waterfront (different from the Seaport). When are you coming?
The 3rd, 4th or 5th closest?