This was an almost total Steve Marriott composition, although, as usual, attributed to Marriott/Lane. Steve said that it was written for his first wife, Jenny Rylance, who he had wanted to marry for several years, but she was Rod Stewart's partner. Eventually, Jenny left Rod, and, at first relictantly, began to date Steve.
Steve wanted to give it to pp Arnold, who is in the clip, but decided to keep it. Pp, by the way, was another of Steve's lovers, just before he moved in with Jenny (consequently, she didn't like Jenny).