The way I see it, this scenario offers 2 choices:
1. you can tell them, but more then likely they are going to try and save, comfort, help you. It's very hard for a non-suicidal person to understand our pain. If you're not sure about your CTB, have second thoughts, you have hope, then I think that telling them is the right thing. Everyone needs help there is no shame in asking for it. And there is no shame in accepting it.
2. Not tell them in which case you'll feel guilty, and all the lies and pretending will be painful. This is my option at the present time. As I feel like I don't have much time left, I opted to speak to my parents 3 times a week via video chat (they live in another country), tell them I love them very much, tell them I'm fine, help them with daily life from a distance etc. In the suicide note, I made a section specific to them explaining my reasons, transmitting my love, reassure them that this is what I wanted and this is the best course for me.
I tried to live for others but I don't have the strength left to go on. For them not to suffer I had to suffer and I carried my cross for as long as I could, it's just too heavy now and I can't no more.
Consider yourself as the centre of the universe, just one time, and see which sacrifice makes you happy: sacrificing your life or sacrificing your fear of telling them and get help.