这句话中,so是副词吗?“i should have ……done that“中是虚拟语句吗,this和that有什么区

这句话中,so是副词吗?“i should have ……done that“中是虚拟语句吗,this和that有什么区别?
one of the reasons i did want to write this book was so many people are on the sidelines saying i should have done this or i would have done that or in some way taking about my life whithout having lived it,and i have.