Trust me on this one -- your boss wouldn't hesitate to sell you down the river if it benefited him. Having had bosses I thought cared about me who then turned out only to care about anything BUT me, my hard-won advice is: Do what's best for YOU. If changing jobs will make you happier, then do it. No matter how indispensable he may tell you you are, the sad truth is, ain't nobody indispensable except possibly the person who founded the company.

Follow your heart and quit stressing.