My boyfriend broke up with me and we live together. How should I act if I want him back?

He is currently seeing someone else. I know that it is just a rebound but we just split up a couple of weeks ago and it is really painful to see him "moving on". I know that he still wants to be friends but I think that if I can make him miss me he will want me back when his rebound relationship goes sour. What should I do?