能不能把 to tell you the truth, I don't believe him.改成 telling you the truth,...

不能.to tell you the truth 放于句首是作插入语.不定时常会放于句首作插入语,比如,to be honest, you are a little lazy.能再解释的详细一些吗?不是独立主格。独立主格指的是有和句子不同的主语。比如，weather permitting, we will contiue our sports meeting. weather permitting 是独立主格。