i feel just cause he cheated , you should not cheat . Thats the worst mistake. He may have a problem due to whioh he may be doing this , something that needs counselling . But I trully feel if you are trully in love maybe you can make a mistake once but not 5 times. But then its up to u to decide . talk with him . You really dont want to spend your life with him if he is cheating you always. And the worst part is its a cycle. Lets say he has a deep seeded problem and he is trying to work it out and you feel suspicious (which you will) and he might not even have done anything but you will still not believe him . Its complicated. the answer has to come from within and stick with it (sometimes thats too difficult). If its cause of some emotional or physical problem he had in his childhood or a psychological problem then try and seek help. Also I guess teh kind of people he is moving around with might also be a problem . it could also be peer presure , teh point that he lacks strong will power but then thats not an excuse.
Also he may think he is secure and that you may never leave him cause you love him so much . Also the fact that he is willinng to leave you if you ever cheated , (considering the fact , that he has doen it so many times) is a bit dicey.
You will find love . Love is not someting whichn only comes once in our lifetime. You dont have to stick around and kill yourself from within , and maybe feel guilt as to why someone you love so much may cheat on you. Its not you. But to cheat and to say I did so cause he did so is wrong and totally not acceptable (for you and not us). you are accountable to yourself and no one else. But one should not fall in teh trap of becoming and doing what one hates in teh first place. you will always loose that way.
telling the truth can sometimes backfire , but in this case a good explanation of teh reasons might be fine. It will allow you to feel less guilty and if he leaves you then it will be for the good cause you then dont need him .
Also try and see as to why you you are still sticking around . What is the thing that you are holding on to , what is it that you are hung up on . Do you love yourself , are you confident are you happy . I might guess not . dont fool ypourself . Sometimes we cling on to somethings and say thats causing me great pain when there was no need of feeling that pain in teh first place. solve whats inside you and the rest will get sorted out .
Merry Christmas and wishing you a very Happy New Year with guidance and blessings showered on you .
(I have written all this very fast so pardon any spelling mistakes. )