Here you go.
Elena, nice job but even you made some mistakes, mainly with commas as punctuation is especially hard in Russian.
Also some spelling (case mistakes also but sometimes those can be spelling, you just don't know it's cases) and just speech mistakes and I hope you notice the changes I made.
Привет Дорогая,
Как дела? Я понимаю, что у тебя изменилась жизнь. Надеюсь, что тебе очень нравятся твои новые друзья и новый парень. Я пишу тебе по разным причинам. Цель этого письма, поздравить тебя с Новым Годом. Время, которое мы вместе провели было просто удивительное! Я тебя никогда не забуду.
С Новым Годом и дo будущей встречи!
Remember commas most always go before что and Который (in all grammatical case declensions) and separate two clauses in a compound sentence. In Russian there is also no Oxford comma although in English it is a debated issue and goes either way. Russian along with German have challenging if not the most challenging comma and punctuation systems so I appreciate everyone's effort :)
Hope I could help!
-Артур
Edit:
Elena, НОВЫМ ПАРНЯМ is plural dative while in the sentence it is supposed to be singular instrumental because the preposition "C" is used. Therefore, it should be НОВЫМ ПАРН(ЕМ), although I changed that sentence.
ДРУЗЬЯМИ you also misspelled ДРУЗЯМИ, missing "Ь".
You also said ДО БУДУЩИЙ ВСТРЕЧИ. Будущий is supposed to be genitive because of the preposition ДО.
Therefore, it's ДО БУДУЩ(ЕЙ) ВСТРЕЧИ.