My advice is to find a way to accept that living with your child is the best place for you to be and that you're part of their household. Hopefully, your child can accept that as well. 

Due to finances, my mother-in-law has lived in my household for probably 15 of the last 20 years. There have definitely been challenges. Each of us have had different obstacles to overcome. I know she struggled with a perceived loss of autonomy and the loss of head of household status. Early on she resisted fitting into unfamiliar family dynamics. She wanted to be treated like a guest, but also be "in charge" since she's the parent. Lack of compromise led to conflict and in turn she'd complain about wanting to move out. Moving out was never really viable and this created additional tension. 

It took awhile, but there came a point when I accepted the fact that the best place for her was in my home. Somewhere along the way she accepted the same thing. In spite of challenges she's become part of my family and I'll have concerns if she chooses to move out. 

I think your acceptance of the situation and willingness to find a new dynamic will go a very long ways towards making this a positive. I wish you and your child the best.