I want half but don't want to do ant work

[Donna Dwyer]

My boyfriend owns a home with his ex girlfriend. It was bought as a tax sale. He has been the only one putting money into the home for remodel and repairs all with his own money. He works all day then goes to the house and works on it until 8pm. He is paying all utilities and taxes. 

He has the house almost ready to go up for sale. Now after not doing a single improvement on the home the ex wants half of the sale amount.

There was no agreement in place when the house was purchased as to what would happen when it would be sold.

Legally how would this be approached.