@finally_me You mentioned wanting to "ask them out," but beyond that it's not clear to me what your current relationship (using that word generically) is to this person or where you want to take things.
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Some things to consider:
If this is someone who's currently a friend to you, are they a good enough friend that you'd trust coming out to them as poly, and to keep that to themselves even if they don't want to develop a deeper sort of relationship?
If this isn't someone who's a friend to you now, is developing that sort of friendship something you're willing to do "for your own safety" (to avoid coming out more broadly)?
Would you still want to date someone who didn't know you were poly if that knowledge would "blow up your chances?"
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My approach:
I'm not *generally* out as poly to my friends, family, or coworkers. There are a smattering of exceptions, and those are people I developed strong enough relationships with that I trust them to continue to want me in their life and to keep my poly identity to themselves. Right now, this feels like the right balance; I acknowledge that might change in the future.
Personally, I'm very against the idea of building a deep relationship (beyond "friend" or "acquaintance" labels) without being transparent that I'm poly. For better or worse, monogamy comes with a handful of "scripts" and assumptions, and I've found some of those don't align with my values. Building an assumed-monogamous relationship would mean pushing my values (my authentic self) aside, consciously or unconsciously. I've already done that once, unintentionally, and I would *not* recommend it.
"Asking someone out" and dating in general is another one of those things that has a bunch of "scripts" and assumptions baked in. Polyamory isn't part of the socially accepted dating "script," unfortunately. I don't feel like there's just one way to account for that difference, but I feel like any indirect approach would involve a ton more work/risk/pain for everyone involved.
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For the record, coming out as poly to *anyone* is scary, and confessing attraction to someone or asking someone out adds another layer of that. I think you're justified in feeling terrified…and I think there are some amazing people out there who are worth facing that fear for.