'You are not the boss of me' is perfectly grammatically correct, if a little antiquated in usage.
You can say 'my boss' with equal correctness.
Here are some more examples of the possessive:
my friend's mother = the mother of my friend
your friend = the friend of you
our friend - the friend of us
In such examples, 'of' is a sort of abbreviation for 'belonging to', so these phrases could be said as
the mother belonging to my friend
the friend belonging to you
the friend belonging to us
Or, to carry it a step further, 'belonging to' can also become 'owned by', as in:
the mother owned by my friend (etc)
Of course, nobody would say that about a person, but if you're talking of other things, it can be quite correct, as in:
the car owned by my friend = the car belonging to my friend = my friend's car.
An apostrophe (') can indicate ownership (the possessive case), as in the following:
my friend's boss (the boss of my friend)
his neighbour's house (or if there is more than one neighbour it becomes 'his neighbours' house)
your husband's sister's daughter's child (the child of the daughter of the sister of your husband)
Note: there is no apostrophe in the possessive "its". Take a close look at the following sentences. The apostrophe in the second sentence indicates a missing letter. It stands for 'i', as an 'It is'. 'It' is the pronoun which stands for 'the cat'.
The cat lost its tail. It's in pain.
The rule of possessiveness has nothing to do with ending sentences with a preposition. A preposition (look at the word closely - pre-position - 'put in a place BEFORE') is different from a 'personal pronoun'.
Examples of prepositions: to, by, above, before, after, towards, of, along, and about a zillion others. Examples: 'to the shop', 'by the river', 'above your head', 'before dinner', 'after the storm', 'towards the east', 'of the family', 'along the road'.
Examples of personal pronouns: If the person is the subject of the sentence, the pronoun will be: I, you, it, he, she, they. If the person is the object of the sentence, the pronoun will be: me, you, it, him, her, them.
I (subject) gave the book to you (object).
You (subject) gave the book to her (object)
They (subject) gave the books to them (object)
Note the following sentences:
"My husband and I received gifts." (In this case, both 'my husband' and 'I' can begin the sentence, so you'd say 'My husband received gifts' or 'I received gifts'. This is a sentence with two subjects.
"Gifts were given to my husband and me." In this case, 'gifts' is the subject, and 'my husband' becomes an object', as does 'me', because they come after the verb and a preposition'. Again, you can make two sentences out of the one: 'Gifts were given to my husband'. 'Gifts were given 'to me'.
You would never say 'Gifts were given to I', or 'Me was given gifts', would you?
Equally, you'd never say 'Gifts were given to they', or 'Them were given gifts.'
The personal pronoun changes according to where it is used in a sentence.
Pronouns are used to replace nouns or names, where the use of those can become cumbersome.
"I" can replace the full name of a single person speaking about him/herself.
"You" can replace the full name of the person another person is speaking to (or to put that more grammatically correct "....to whom another person is speaking"!) As in: 'You are my friend' stands for 'The person to whom I am speaking who goes by the name of....... is my friend' (the friend of me, the friend of myself known as .....).
Pronouns can be singular or plural. A single person is 'I'. More than one person is 'we'. He, she, it are singular pronouns, and in the plural they become 'they'. 'You' singular remains 'you' plural.
When the pronouns become objects of the sentence: "I" becomes "me"; "You" remains the same; "He" becomes "him"; "she" becomes "her"; "it" becomes "them"; "we" becomes "us"; "they" becomes "them".
As in:
I am a girl. (first person singular) We are girls. (First person plural)
You are a girl. (second person singular) You are girls. (second person plural)
He is a boy. (third person singular). They are boys. (third person plural)
It is a cat. (third person singular) They are cats. (third person plural)
She is a teacher. (third person singular) They are teachers. (third person plural.)
He plays football. (third person singular). They play football. (third person plural)
He goes to school. She goes to school. They (all) go to school.
He gives the ball to him.
I give the toy to you.
They give the toy to us.
We give the toy to them.
You take the toy from me.
She takes the toy from us.
This is my toy. This is your toy. This is his toy. This is her toy. This is their toy. These are his toys. These are their toys. These are our toys.
This is the toy of me. This is the toy of you. This is thetoy of him. This is the toy of her. This is the toy of them. These are the toys belonging to him. These are the toys belonging to them. These are the toys belong to us.
PLEASE NOTE: apostrophes NEVER indicate plurals!!! potato/potatoes; jelly/jellies; mother/mothers; toy/toys; 1960s; MP3s. Etc. I cringe when I see a sign saying 'Apple's for sale'. I always ask myself 'the apple's WHAT is for sale? What belonging to the apple is being sold?
These are things I was taught in the first few years of my schooling. I studied it in much greater depth at university. It's a pity not much of this sort of thing is taught at any time these days.