Checks and Balances

So, I’ve been getting myself edjumacated on the Gay Marriage issue, and I’m a bit confused on how the government system works in our state. So, I’d appreciate someone helping me figure out how the process of legalizing Gay Marriage in Massachusetts worked.

• The Massachusetts SJC decided that the Marriage laws in Massachusetts were unconstitutional. How do they manage to tell the Legislature to change it? Had they not changed the laws, what would the consequences have been? If Gov. Romney had vetoed the change, would he have been held in contempt of court?
• It’s my understanding that government branches are set up as a system of checks and balances, to keep any one branch from having too much power. In this case, the courts were changing what the Legislature was doing. What’s the system in place to keep the courts from having too much power? That is, since I’ve been disagreeing with the decisions that the courts have been making, what actions can I as a citizen do to try to keep the courts in check? (I understand that this may be indirect. I think I’m looking for an answer of the form “Vote for candidates for office X that support doing Y.”, but I’m not sure.)

I’m primarily focusing on the state level of government here, but input on the federal level is also appreciated.