Do myself and my strictly roomate of 3 years have to claim common law? we have filed as single in prior years. only one of us is eligible for the gst credit,

If you are not common-law partners, then don't claim that you are. 

In your case it won't matter - the GST credit can only be claimed by one spouse/partner anyway. Claiming common-law might even hurt you since the GST credit is based on your family net income. If you're incomes are joined together, you may make too much to get it.