Please let him go from your life..You will have a better life to think about other things than this relationship.
Trust me you boyfriend will never forgive you for being with his friend even for few months. Also the details which you have mentioned in the mail makes it clear that even you know that he is not “The BEst ” for you. Even you dont trust him”… so let him go girl…and be alone for sometime. Enjoy your freedom, you deciding for youself, not being answerable and also plan for your life ahead….