Shouldn't that be ٌرَفِيْق(rafeequn) and ٌرِفْق(rifqun) respectively for the two. Additional ي between ف and ق is not for case, but it is used to indicate that it is for adjectives, most of the time.
This is not correct, the proper translation for 'my friend' is 'Rafiki Yangu'. 'Friend' is one of the fee exceptions that belong is the family noun class there for you use 'yangu'