My advice is if you have not start the relationship, dont start. If you have started the relationship, put a stop to it before it goes deeper. Since you are asking for advice in this forum, it shows that you are hesitant to be a third party. If this man can bear to betray his wife despite her bearing two sons for him, what can you offer him to ensure that he will not betray you in future? It will not be easy to let his two boys accept you and how prepared are you to b a step mother. You will b labelled as a third party and is not worth to live your life like that after your own failed marriage. Find a more worthy man to love than to love other woman's man. Tell yourself that you deserve someone better.