Can I file my tax return stating that I am common-law with my partner when he filed his return as a single person? He forgot to add me as his partner.

[TurboTaxBrenda1]

If your marital status is common-law yes you will enter that you are common-law

"Living common-law" means you are living with a person who is not your spouse, but with whom you have a conjugal relationship, and to whom at least one of the following situations applies:

1. They have been living with you in a conjugal relationship for at least 12 continuous months.

   Note
   In this definition, 12 continuous months includes any period you were separated for less than 90 days because of a breakdown in the relationship.

2. They are the parent of your child by birth or adoption.
3. They have custody and control of your child (or had custody and control immediately before the child turned 19 years of age) and your child is wholly dependent on that person for support.