每個人在變

在第一天開學，每個人在單獨（都是獨自一人），沒有朋友，對呢（吧）？好不容易終於找了朋友們。然後，一段時間後，每個人卻都變了，不是以前的自我（己）。朋友們和你再也不是以前的你們, 也不再那麼的相似一樣再也。你再次單獨（變成一個人）。直到找到別的人跟你有類似的喜好利益為你。但是我們天天在變。怎麽可以有永遠的好朋友們？
我最近逐漸認識了解到我前時候（以前）的朋友們經常（已經）跟我不一樣。我變了，我再次單獨一人。

如果看不懂：On the first day of school, everyone is alone. No one has friends, right? Eventually, finding friends. Suddenly, everyone changes, not their previous selves. [Your] friends and you aren't like each other anymore. Again by yourself. Until finding friends with similar interests as you, but everyday we are changing. How can [we] have friends that last forever?
A recently came to realize my friends from before and I now aren't alike. I changed, again, I'm alone.

You did a really good job!  I can easily understand what you were trying to say.  

Only few mistakes:

(1)呢 is used when you are really confused about something.  If you already had a thoughts and want to ask people if they agree with you, it's better to use 吧（same as "right?"）

(2)

朋友們和你（your friend and you）再也不是(are no longer)以前的你們(the people you used to be)

也(and)不再(are no longer)那麼的(being so)相似(similar)

(3)

跟你(as you)有(has)類似(similar)的喜好(hobby) : who has similar hobby as you

(4)

認識 means "know （a person）" 
For example: 我認識他（I KNOW him） 

了解 means "understand and realize"

For example: 我了解了（I got it）  我了解到他已經變了（I realize that he has changed）

(5)

經常 means "often"

For example: 我上學經常遲到（I'm often late for calss） 遲到 verb. being late

已經 means "already"

For example: 我已經很累了（I am already very tired）

Purple parts are something native speakers like to use:

(1)單獨 does mean alone, but, in this situation, we like to use 獨自一人 which also means alone.

(2)we like to use 好不容易, when something is not easy to do but we eventually solve problem or achieve the goal.

(3)自我 is sort of formal. For eample: 自我實現（this is a term in psychology: self-actualization）

In daily live, we usually use “自己”  For eample:他自己（himself）我自己（myself）

I know some of my English explainations may be weird.  I apologize for that. Hope this is helpful for you.  If you have any other questions, don't hesitate to ask me:)