My dear, listen to your heart: you feel he is still taken by his ex. It is probably true. You say he had several indiscretions in the past, what else do you need to know? If he does it now, what will he do once you are married? D-u-m-p him.
Our Agony Aunt is a Life Coach and Relationship Coach as well as a Corporate and Organisational Consultant. AA lives and works in Bangladesh but travels extensively around the world to give seminars and to see her clients