You are making an assumption hiding the truth is better for your sister. She is asking for the truth. If I were her I would want the same as it hurts far more to be lied to.

Is it possible you are hiding because it is easier for you to behave like you want when she doesn't know? In the past you've indicated it is somewhat of a thrill to keep the info hidden.

I would take a step back from your behavior and look at the true motivation behind it. Only then can you know if your actions are selfish. If you look and see that you are behaving in a way that puts your needs before what she is asking for, you potentially have an issue. Sometimes we need to put ourselves first, but if it is chronic and against her wishes, it might be time to make a change.

You can always answer truthfully without laying your personal information bare. It is perfectly ok to tell someone you don't want to share how you're doing or feeling. Maybe there's a way to protect your privacy and meet her needs as well. It doesn't need to be either or. Integrity is always worth a second look. Much love to you as always Miss Laura.