There were several reasons why he would merit from kept silent about it.
彼がそれを黙っていることにはいくつかメリットがありました。
There were several reasons why he would merit from kept silent about it.
メリットがある＝he would merit from
まず、友達を裏切らなくてすむ
First, he wouldn't have to betray his friends.
つぎに、嘘をついていないので、後々気が楽
Secondly, he would not be lying, so he had no twinge of conscience.
気が楽⇒良心の呵責がない＝no twinge of conscience.
また、色々しゃべってボロがでるということを避けらることなどです。
Furthermore, he could avoid being caught tripping after saying too much.
ぼろが出る＝be caught tripping over XX
日本 
