Yes, my partner knows. I've declared many times in the past that, "When my baby girl goes, I go."
My baby girl crossed over the rainbow bridge almost a year ago. He knows I've been secretly planning my CTB.
He's a normie, and so he cannot wrap his head around it. His reactions have been all over the place, from ignoring my suicidal ideations, to being in denial that I'm quite serious about it, to strongly proposing that I go back to seeing my therapist, etc. etc. Other days he'd be quite angry and confrontational. Just a couple of days ago, he threatened to tell all my family about it. Today, he's been all sweet and gentle.