1.Happiness is like a pebble dropped into a pool to set in motion an ever-widening circle of ripples.

这句的主语是happiness, 谓语是is like, 宾语是a pebble, 后面的dropped into a pool...是分词做定语，修饰a pebble. “to set in motion an ever-widening circle of ripples”是不定式

做定语，修饰a pebble.

2. Before long与long before的区别：Before long意思是“不久以后”；long before意思是“很久以前”。
例句：
It looks as if it will rain before long.
看起来一会儿就要下雨了。
I knew Tom long before I knew you.
我在认识你之前很久就认识了汤姆。