This is all can say if i wr you..Try to ask yourself? Are you willing to lost him or not? If u cant accept losing him in ur life, you have to control urself not being jelous.Thus, do and give the best in you to him.Show to him your much more better than anybody else.By doing that, he can now compare and makes him think that your worth keeping than anybody else.Make urself not only his lover but also a best friend to him.In that way, he has no more reason to seek it from somebody more than you could do to him.Stop nagging about your jelousy to his ex. He will feel guilty in the long run.If theres a time that ur really feel so hurt inside, dont say or tell him"dont do it" , better tell him in a right way that makes him feel guilty..If he still goes on hurting you, and you think not reasonable anymore, coz u did your best already, better feel sorry for yourself ang move on.Goodluck to you....
