I may be way off base here but going to say it anyway. If you feel the need to tell your sister and it will ease your stress or make you happier then you should do it. If your sister does not accept you for who you are then know that the problem lies with her not with you. You being honest with someone you love about something that is important to you is a good thing. The thing that a person who loves you SHOULD do is to be grateful that you are trusting enough in their love to be honest with them. I do hope your sister gives you the acceptance, love, and support that you deserve.