I want to cut my hair--我想剪头发

I found I shed so much hair when I was washing it. I don’t know why I usually lose my hair during the summer. Every time I caught the sight of the hair twining my fingers, there was only one impulse of motion to action—getting a haircut—but I thought also that despite the difficulty of my keeping the hair so long, I was not willing to cut it. When I wore short hair, people around me said it was not beautiful as the long one hair and a little childish and boyish. As a matter of fact, I like the short one hair more on account of the simple hair care. I might go out without combing it when in haste. Hehe.
In college, long hair is one of the essential features for a belle. The one who wears short hair will be recognised as coming from the physical culture institute or a bookworm.

If you are talking about your hair, you cannot call it a "the/a short one" or "the/a long one." If you are talking about a haircut (or style), you can. Loose is the opposite of tight, the meaning is different from lose (something that has been lost). 

洗头的时候发现我掉了好多头发，我不知道为什么我老是夏天掉头发。每次看到缠在手指上的头发，就只有一个想法—将头发，但是又想想好不容易留那么长了，就又不舍得剪了。我留短发的时候，身边的人都说，没长头发好看，还孩子气和男孩子气。其实，我更喜欢短发，打理起来简单，有时急着出门，我都不梳它。嘿嘿。
在大学里，长头发是美女的基本特征之一。留短发的会被认为不是来自体院，就是书呆子。

I want to cut my hair--我想剪头发

I found I shed so much hair when I was washing it. I don’t know why I usually loose my hair during the summer. Every time I caught the sight of the hair twining my fingers, there was only one impulse of motion—getting a haircut—but I thought also the difficulty of my keeping the hair so long, I was not willing to cut it. When I wore short hair, people around me said it was not beautiful as the long one and a little childish and boyish. As a matter of fact, I like the short one more on account of the simple hair care. I might go out without combing it when in haste. Hehe.
In college, long hair is one of the essential features for a belle. The one who wears short hair will be recognised as coming from the physical culture institute or bookworm.

洗头的时候发现我掉了好多头发，When I wash my hair, many fell. 

我不知道为什么我老是夏天掉头发。I do not know why this is so, especially during summer.

每次看到缠在手指上的头发，就只有一个想法—将头发，但是又想想好不容易留那么长了，就又不舍得剪了。

Each time, I see strands around my hand, my first impulse - cut them!  However, on the second thought, I could not bare to see my lovely long hair gone since growing to such a length is not an easy thing to do.

我留短发的时候，身边的人都说，没长头发好看，还孩子气和男孩子气。When I had short hair, others would comment that it is unbecoming as I look like a kid or worse still, a little boy.

其实，我更喜欢短发，打理起来简单，有时急着出门，我都不梳它。嘿嘿。 Actually, I like having short hair even more as maintenance is so much simpler.  When I am in a hurry to go out, I don't need to comb it. Hee, hee.
在大学里，长头发是美女的基本特征之一。留短发的会被认为不是来自体院，就是书呆子。

On campus grounds, long hair is a badge of a pretty girl.  Thus having short hair can be a sign that if you are not a sports major , then you are a bookworm.