Preposition Rules
There are 2 major rules when it comes to the use of prepositions.

The first major rule deals with preposition choice. Certain prepositions must follow certain words, and the correct preposition must be used to make relationships between words in the sentences clear. The second major rule deals with the prepositions place in the sentence. Prepositions must be followed by nouns, and prepositions can only go on the end of the sentence in certain situations. 
then please i m sorry for chatting with u but will u be my freind???????
yes.......i love to be....:)
then please thank u its my pleasure............
but please can u send me freind request because i am unable to do so..........
Here are some general rules regarding prepositions:It is permissible to end a sentence with a preposition.A preposition is followed by a noun.A preposition is never followed by a verb.It is permissible to begin a sentence with a preposition, or a prepositional phrase, but be very careful when you do so.*A prepositional phrase always begins with a preposition and ends with a noun or pronoun called the OBJECT of the preposition.The subject of the sentence can never be part of a prepositional phrase.A verb can never be a part of a prepositional phrase