by一点小问题

是起强调作用的，强调他承认窗户是他自己打破的。

应该表示一种主动承认错误的倾向吧。具体用法还得问专业的人

就是由他自己的意思
我觉得是
你自己看看吧

介词by可以用来表示方位、时间、手段等,其用法在高考中曾多次出现。下面结合高考试卷和其它一些例句做一下归纳：
一、by+地点名词。表方位，意为：“在…旁边”。如：by the lake/river/tree/window/door等。
She searched the top of the hill and stopped to rest on a big rock by the side of the path.(NMET90)她搜索了山顶，然后停下来在路边的一块大石头上休息。
After supper she would sit down by the fire,sometimes for as long as an hour,thinking of her young and happy days.(2003上海·春）晚饭后，她常坐在火旁，有时长达一个小时地回忆她那青春、快乐的年代。
注：有时可表:“从…旁经过”,多与动词go/walk/pass等连用。
As we boys were rushing towards the playground,Jim slipped by the table.(NMET92完形）当我们这些男生冲向操场时，吉姆从桌旁溜过。
二、by+时间名词。意为：“到…时（已发生某事），此时谓语多用完成时；最晚、不迟于…，在…之前”。如：by now/then/this time/next Friday/the end of/three o`clock等。
By the end of last year,another new gymnasium had been completed.(2003上海·春）到去年年底，又有一座新体育馆峻工了。
The train leaves at 6:00 pm.So I have to be at the station by 5:40 pm at the latest.(NMET97)火车下午六点开，所以