Most Helpful Guy
There is nothing you can do. And if you could pull it off it just shows his character of changing anytime the wind blows.
Most Helpful Girl
you can't... he'll break up when and if he wants to... and if you truly love him and want him back you need to do what's best for him. you could be his friend for now, but don't have any expectations in mind. maybe eventually they will break up because of their own reasons and then you can flirt or tell him how you feel.