This is one of a number of songs written by Eric Clapton for his former wife (and George Harrison's former wife), Patti Boyd. Other Clapton tunes inspired by Boyd are Layla and Wonderful Tonight. Harrison's most famous paean to Boyd is Something.
Why Does Love Got to Be So Sad? exemplifies a genre of tunes I call sad longing songs. Despite that, the song manages to somehow be jubilant, if a bit overlong. I suppose that's true to the experiences attested to by sad longing song: There's jubilation in love, sadness when it can't flower or be expressed. That makes this song a kind of resigned, wondering, and yet, jubilant celebration of love's entry into one's life, even love that can't be. Unrequited love can be exhilarating and shattering at the same time, though it makes no sense that that should be the case. At least that's what this song seems to say.
Clapton originally recorded Why Does Love Got to Be So Sad? in 1970, while he was a member of Derek and the Dominos.
This is a live version recorded by him in 2009.