His new body won’t change your relationship
His getting in shape won’t change your relationship. Your bond is stronger than that. You connect over more than food. If his getting in shape does cause a rift between you two, that’s something to analyze closely. It could be a sign that there were preexisting issues in the relationship. It could be a sign that you’re pulling away. But, either way, your partner shouldn’t have to stay in poor health in order for you two to stay close.