Lyric discussion by kindofblue 

Cover art for I'm in You lyrics by Peter Frampton

An equally valid interpretation -

He lives and thrives in her honesty and acceptance. ("when I cry you don't laugh" & "you & I don't pretend - we make love") This is contrasted to a previous love who also gave him the love he never had. This love is real, 'cause she KNOWS him, in every sense...