When You Really Loved Someone by Agnetha Fältskog
the song is about her past love with former husband Björn Ulvaeus, the music video makes it obvious, theres a blonde girl(obviously Agnetha) and a guy(björn) they fight and he leaves and thats exactly similar to what happened to her and björn they had a fight and thats what ended their relationship, you could argue that and say the song is about frida and benny and i mean it very well might be but in all honesty theres a blonde girl and well Agnetha is blonde...