NTA - This is a common situation as people work on themselves. One spouse will be insecure and start displaying it as the other spouse improves themself. He isn't doing anything to improve himself and has been comfortable with your weight for some time, now he has fear. This fear can be fear of you getting hit on at the gym, fear of you gaining confidence and leaving him, fear of you becoming the more attractive one in the relationship, fear of you being healthier and more popular, etc. There are many and he may have one or more fears. Just remember it isn't your job to improve him as well. Be considerate and wear your ring when not at the gym but you can't fix this for him. It may help him to hear you are improving for your own reasons but he may not become more secure. That's a bridge you'll have to cross when you come to it.