关于朋友的英语谚语，综合多个权威来源整理如下：

一、友情珍贵类

1. A friend is easier lost than found. 得朋友难，失朋友易

2. A friend in need is a friend indeed. 患难见真情

3. The friendship of a gentleman is insipid as water. 君子之交淡如水

4. Old friends and old wine are best. 陈酒味醇，老友情深

二、友情特质类

1. Between friends all is common. 朋友之间不分彼此

2. A friend is never known till a man has need. 需要之时方知友

3. A friend without faults will never be found. 没有十全十美的朋友

4. True friendship is not measured by time but by depth. 真正的友情不在于时间而在于深度

三、友情维护类

1. To prepare a friend, honor him present, praise him absent, and assist him in his necessities. 维护朋友需做到：当面尊重、背后表扬、患难相助

2. Love me, love my dog. 多个朋友等于一个帮手

3. Misfortune must be shared, joy must be kept. 困难当共，快乐当同

四、友情变迁类

1. Friends must part. 天下无不散之筵席

2. The more we love our friends, the less we flatter them. 真挚的友情胜过虚伪的奉承

3. The smell of coin is often the knell of friendship. 铜臭味浓往往是友谊的不祥之兆

这些谚语从不同角度诠释了友情的珍贵、特质、维护方式及变迁规律，可作为英语写作和口语表达的素材。