My partner left four and a half years ago. We jointly own the house, can he just move back in?

My partner left four and a half years ago. We jointly own the house, can he just move back in?
Added (1). He stopped contributing to the mortgage in May 2012 and has not paid any maintenance for our son as he says he cant afford it because of his rental costs. We live in Scotland
Added (2). He now wants to return as he needs to recoup some of his costs/outgoings and wants to stay in the house until it is sold

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