Relationship and health

Obviously it’s normal in a relationship to care about each other’s health and well being. small back story: me and my (first) boyfriend are 18 and i’m going to college in the fall and he’s enrolled in the navy and leaving for boot camp in June. we’ve been dating for almost a year and we want to try and make things work out.

My boyfriends sister’s husband was in the air force and my boyfriend said she became pretty depressed from him leaving for deployment and gained some weight and my boyfriend doesn’t want that to happen to me- makes sense. He’s been wanting me to promise i will be healthy and happy for him and by proving to him he wants me to go to the gym and eat healthy (i like going to the gym and my eating habits aren’t the greatest... but i’m trying).

Writing this out sounds stupid of me tbh but am I wrong for wanting a cheeseburger from Wendy’s without getting shit for it? I overall don’t eat that bad but every time i do I feel like complete shit about it because i promised him i’d be happy healthy me when he’s leaves.... i just don’t know. Help ease my mind I wanna know if I’m crazy to think this way or not....