Tldr: I (33m) am bi but closeted to my partner (34f), and would like to come out just so I don't have to live a lie. But what's the point of opening that Pandora's box of questions she'll have about my sexual history, if I probably can't ever get any dick while I'm with her anyway?

Long read: We've been together for 8 years, and about 2 years in I mentioned I had had some experience with a guy before her, and she reacted in a way that made me hold back and lie about how far it went. She said she would like her man to be "all man", ie hetero. Various conversations since about guys' hotness, who we find attractive, hypothetical threesomes, but in all of those I've gotten responses from her in the same vein.

If I come out to her now, I'm concerned that it will lead to a "radical transparency or I can't ever trust what you say to me" vibe. How have those convos gone in our queerlybeloved community? I have some sexual skeletons in the closet that would be unearthed by such an inquiry that would really blow up our spot. Plus I can't just say "I'm tired/stressed" when I can't get it up, instead of "I'm in a gay phase right now so you aren't hot to me." And in the best case scenario where we stay together and she doesn't dig into details and is OK with me not always being into her, maybe there's a threesome in our future with someone we both find hot? I just don't know if it's worth it... Ideas?