You want to file for what is called a 1A divorce (no fault, uncontested).

The forms you need are here:

http://www.mass.gov/courts/courtsandjudges/courts/probateandfamilycourt/forms.html

Also check out this page -- it details everything you need for a no fault, uncontested (1A) divorce:

http://www1.divorcenet.com/ma/chapter5.html