首先，中文里经常把很多小句子用逗号连起来，但英文不可以这么做。每个句子只能有一个核心思想，不相关的句子要用句号分开，因此So long time that I didn't come here, today one of my roommates left my dorm, maybe it's a better thing这样的句子不行。

1） So long time that I didn't come here

这不是这么说的，应该说I haven't been here for such a long time或I haven't come here for such a long time。

2） today one of my roommates left my dorm

3） maybe it's a better thing, because our dorm will be quieter

better是比较形式，你这句里没有比较的意思，所以用better不妥。还是写Maybe it's a good thing。

4) I don't know, but I don't want her to leave for that we are friends.

因为可以写为"for"， 但没有"for that"这个说法，要说"for we are friends"。不过，"for"当做“因为”的意思的时候，很诗意，也不常用，所以你这么用虽然不算错，但很不地道。可以用“because”或者“since”。

I don't know, but I don't want her to leave since we are friends.

5) Different friends have different feeling

要写feelings（复数形式）

6） everytime when I recalled my former friend, I feel sad

时态用错了，前后半句不对应。你想说一般情况吧，那就前半句要用现在一般式:

Everytime I recall my former friend, I feel sad

也不用写when。还有，你的室友离开了就不是你的朋友了吗？为什么要强调“former”？除非你们现在不是朋友了，否则不用说“former”。说时候，我不知道你在说这个室友，还是你所有的以前的朋友，如果是后者，那么要用复数形式，就是friends。

7) maybe I am bound to become strangers to someone, but I never thought I will remember those experiences for my life.

bound to可以是“注定”的意思，但通常是“很有可能”的意思，在这里我不知道你想表达什么意思。这个句子很别扭，但我不知道该怎么改正好，因为我不太清楚你想说明什么。是不是要说"Maybe I am destined to become strangers to some of my friends, but I never thought I would remember those experiences for my whole life"？

8） By the way, a friend of me who I knew from here learned Chinese very well

没有a friend of me这个说法，只有a friends of mine。

9） today I read his journals which are so humours, I hope I can study English continuously.

humourous，不是humours。而且后半句跟前半句有什么关系？独立的句子要用句号分开。后半句是什么意思？我希望我可以不断地学习英语？

不好意思，前面打错了，应该是：

8） By the way, a friend of me who I knew from here learned Chinese very well

没有a friend of me这个说法，只有a friend of mine。