he lie to me again

today my bf lie to me again.he called her again on 3 June 2006 :( he has affair with a girl, call WS. I find out on march... but he choose to back to me... and i take a looong time to accept the truth... and i forgive him. he promise will never happen again.. he will only focus in his career and take care of me.. i trust his word.i not sure my decision will make me regret one more time.. sometimes need someone to advice me..sigh..very sad... long run relationship..is tough..