I think you’re doing a great job in being supportive! Have you ever asked yourself what the exact reasons for him slipping out of his exercise and diet routines are? Perhaps he needs to choose a weight loss diet and exercise plan that suits his lifestyle, personality or needs. It sounds like you are already doing a lot to help him but helping him find something he can stick with might be something you can try. I have been doing some reading and I’ve come across a diet which seems to be working for people, especially those struggling with maintaining their weight loss: it’s the
Dukan Diet weight loss diet for men. Perhaps the weight loss plans he tried before did not really appeal to him; they were only a way to lose weight. Try and find something he wants to and likes to do. This way he will be motivated to stay with it.