he is sincere and easy to get along with.这句话有语法错误吗？with后面不需要宾语吗？

他很真诚并且很好相处。

在be／seem／appear＋形容词＋不定式结构中，动词不定式结构与句子的主语之间有逻辑上的动宾关系或主谓关系。当其为动宾关系时，动词不定式中的动词应为及物动词或不及物动词加介词构成的相当于及物动词的词组。如：
The man is hard to get along with .那个人很难相处。
This room seems too small for us to live in.这房间对我们而言似乎太小了，不能居住。
常见的这类形容词有：easy，difficult，nice，big，large，hard，light，heavy，interesting，dangerous等。

不需要，分解句子就是he is sincere and he is easy to get along with.

句意：他很真诚并且易于相处。
句子没有问题。参看下面内容，需解释再追问。
Sth is easy to do.或find sth easy to do“某些形容词+不定式”的结构中, 不定式与句子主语有动宾关系时，无需使用被动式。(常用于此结构的形容词有：difficult, easy, hard, interesting, pleasant, nice, bitter, fit, dangerous, light, heavy, important等)
The picture is pleasant to look at.
The sentence is not easy to understand.
The street was difficult to find on the map.
Good medicine is bitter to taste.
The novel is interesting to read.
The box is too heavy (for you) to lift.

语法没有问题,with后面不需要宾语,这是固定用法,你可以记一下的.
译文：他很真诚,并容易相处.