No don't tell him he isn't attractive to you, that will probably really hurt him. He also doesn't need to know you think you might be a lesbian, its not really his business. Just tell him you're too busy in your life to date anyone right now, or tell him that while he's a good guy, you just aren't ready to date anyone right now and you hope he understands. He'll get the point. You don't need to go into great detail explaining anything to him. 6 weeks is a fairly short amount of time. Let him down easy and keep it casual, basically the old its-not-you-its-me line, but say it in a way that isn't too cliché.