Complex sentence: Shortly before the album's release, guitarist Peter Frampton left due to growing frictions between him and Marriott, an event which hurt Marriott greatly, though he would never admit it to the other band members.
Split into simpler sentences: Shortly before the album's release, guitarist Peter Frampton left due to growing friction between him and Marriott. His departure hurt Marriott greatly, though he would never admit it to the other band members.