You definitely need to discuss this with him. It may be that while the words he said have some truth, they are not the deep truth.
That being said--people don't like change, and when someone is in a certain 'role' in relation to them they feel threatened when that is different. Many many people who lose weight find that friends or loved ones praise you for the effort, but ultimately feel insecure about it because they have to adapt to the new you.
Hope you work it out!