once a cheater always a cheater?

Do you believe that if a man has a history of cheating it will continue on always? My boyfriend cheated on his ex who he claimed he was "in love with" ; 6 months into our relationship he says he almost cheated but did not cheat. I caught a text of a female on POF saying "it's the man who's gonna fuck you tonight" with ten calls going back and fourth between the two. I tried to leave but he became really suicidal and I did truly love him and wanted to believe it's never happen again - fast forward to 6 months later and I'm not pregnant with our first child and although I don't suspect him cheating now or since that time he was caught, I still worry. Do you believe once a cheater always a cheater?