. Change your appearance
If your SO is a decent human being, they won’t ever force you to alter the way you look for their benefit. They should love you for you, and all of you. If your weight, hair, or style really bothers him, he’s clearly not with you for the right reasons. Any physical changes you make should be made because you want them, not for attention or for someone else.
Don’t change who you are for anyone but yourself. And if you do decide to make any self-adjustments, they should be improvements that will better you. It’s possible that he’d be more interested if you do x, y, and z, but he wouldn’t genuinely like you for you. Never lose sight of who you are.