I still don't understand why two people being in a sexual relationship is considered anyone else's business, or relevant to financial obligations toward minor children.
Because a bursary is essentially free money, given only to people that really need it, so they need to means test it.
When you are couple living together you are jointly responsible for your household income and expenditure. So if OP was a millionaire, do you think it would be morally right for their household to claim free money (on the basis of poverty) for a dependent who is living in their care?
If OP lived with her brother, or some man she works with, or a random who answered an advertisement, would the bursary office be going after them?
No, because it is only parents, step-parents, or the the husband, wife, civil partner or cohabiting partner of one of the student’s parents.
If OP moved out, or if they broke up, the assessment would be re-calculated.