Question about a bible prophecy. John 16:7?

[Mark90]

"Nevertheless I tell you the truth; It is expedient for you that I go away: for if I go not away, the Comforter will not come unto you; but if I depart, I will send him unto you" john 16:7

I'm confused about scholars understanding of the above verse. First, why the holy ghost won't come unless Christ go? He was already guided by the holy ghost which descended upon him. The bible mentioned other people who received the holy ghost like Zcharias, Mary, Simon, etc,. so why it won't come unless he go when it was already there before him and was with him during his life?
Secondly, it has been over 2k+ years and we haven't seen any glimpse of that prophecy? Why it's taking such long time?
finally why would Jesus call it the comforter? Why didn't he just call it the holy ghost?

P.S : I'm not mocking the bible or trying to get a rise out of anyone. I'm just trying to be a good Christian. I have been reading the bible for several days, but I'm a very analytical person so if I read anything that doesn't seems to make sense to me I will ask about it
Thanks.

[DennisC]

If you go to the book of Acts, you will see Jesus' prophesy fulfilled within 50 days of His ascension into heaven.

[Truthfinder]

14:16, 17; 16:7, 8, 13, 14—When referring to the helper, or the spirit of the truth, why is the pronoun “it” used at John 14:16, 17, whereas “him” and “he” are used at John 16:7, 8, 13,*14? The reason for this is strictly grammatical. In the Greek language, in which John’s Gospel was written, the word for “helper” is in the masculine gender, but the term for “spirit” is neuter. In recording Jesus’ statement, John therefore used the masculine pronoun, such as “he” or “him,” when referring to what the helper would do. The neuter pronoun “it” was employed when reference was made to what the spirit of the truth would accomplish.

[element_115x]

Why do you immediately assume that the 'comforter' is the Holy Ghost, hmm?