Dissolving a civil union is not a divorce. That is because a civil union is not a marriage. It is a marriage-like legal construct that had all the rights of marriage sans the actual title.
Because of this, there are no forms like there is for a divorce in Massachusetts.
What to do
You still file for a dissolution in your local county probate and family court - just like a divorce. However, what you'll be filing is actually an equity action in the probate court. You are asking the probate court to exercise its equity powers to void the civil union and deem it broken.
You still need a separation agreement, just like a divorce. You'll also need financial statements, just like in a divorce.
How to wite a complaint in equity
Unfortunately, it's beyond the scope of this legal guide to teach someone how to write an entire complaint in equity for a dissolution of a civil union. Needless to say, it's similar to filing a lawsuit in the Superior Court.
Whereas there are forms you can get from the courthouse for a divorce, there are no forms for dissolving a Vermont civil union. Therefore, it's probably wise to obtain the services of an attorney who has had experience with this special type of "divorce."