I read some books the cover of which are yellow
with years.此处的the是表伴随吗？

I read some books of which the cover are yellow with years.

我把词的顺序调了一下.这是一个定语从句了.注意,分成两句应为:
I read some books

the cover of the books are yellow with years.

book是先行词.

意思是：我读了一些书，那些书的皮因为年久的缘故都黄了。

with 确实是“伴随”。如果必须生硬一点理解的话，定语部分的理解应为：

那些书的皮随着年份的增加而泛黄了。

看看，这是伴随了吧。