I would think

-im = my 

-in = your

-sin = you are

-imsin = you are my -

kankımsın

See http://www.turkishclass.com/turkish_lesson_121 on ´to be´ 

and http://www.turkishclass.com/turkish_lesson_239 on posessive pronouns.

im can be my. It can also be I am.

Yes but here it´s ´my´. Because it´s followed by something else.

it can have 2 meanings.

aptalım = my stupid

aptalım = i am stupid

As you could see aptalım have 2 meanings, but it not works like that everytime.

now i will give you example with word deli which mean crazy. 

delim = my crazy (you can say like that to someone who is close to you)

deliyim = i am crazy

in this example delim have only 1 meaning, and there is big difference between delim and deliyim.

there is only word kanka, but girl said kanki because she wanted to sound more cool.

meaining of can is always same, but of course in english it´s better to say sweetheard. ´Can´ literally mean life as i said. Also hayat mean life, but there is some difference between them.

kedinegro- is it kanka the proper word ! Thanks! Awesome answer harika. I am happy for the responses on the verb ending im from everyone. It helps to understand Turkish more clearly! I will study these answers a couple of times !

Can you use the word kanka when you know someone a short while or is this a word for friendship when you have really known a person for a long time. Such as old friends.

"Kanka" is the short form of "Kan Kardeş", which means blood brother.  In fact it must be used only for best friends but today many people use use it for all friends. 

Another word similar to kanka is "cankuş", that also means best friend.