No and never A guy and girl can never be best friends in terms of spiritual friendship. There will be sexual relationship in that friendship, so if they are in love it's cool but if they are just friends they are cheating to their beloved ones. However its good to have best friends, For a guy, u enjoy having sex with girl u r not marrying and if u r a girl then u enjoy having sex with a guy and sharing other things that u cannot share with ur bf. This happens.