How do you make a man regain interest?

Improve yourself. I'm sure over the years you've gained weight, you don't dress to impress, you sleep in sweat pants, you don't shave your leg each day. You probably nag him. And you ask yourself why should I change? Well, haven't you changed from the time you first got together to now? The person that isn't sexually interested can't just force themself to be interested. You've got to improve yourself physically, emotionally, personality, etc.