Hey there! Hope it's okay that I'm jumping in. I want to validate that there's nothing wrong with you for thinking about other people or feeling bummed or frustrated that your partner's sex drive is different from yours. This is definitely a weird, intense time to make big decisions, so I think it's good that you're going slow and feeling out all your options.
If I had to guess, I'd say that telling Dani that you've always been interested in them wouldn't make you stop thinking about them, but might be some part of you wanting to see if they feel the same way or wanting to start a flirtationship with them. Maybe I'm projecting, because I've had that experience of thinking, "maybe if I tell them I have a crush on them, I'll get over it," but that's never worked for me. And that's okay! I love flirting, but I'm also in a very intentionally nonmonogamous relationship where I talk to my partner about people I'm interested in, and we work through any jealousy, loneliness, or excitement and encouragement that come up as a result of being interested in someone else.
I'm hearing a lot of self-awareness from you about why you might be interested in Dani, which is awesome: that they are far away so commitment feels super low, that the world is on fire so you want something to distract from that, and that you don't know them well so are interested in them conceptually. That doesn't mean you shouldn't pursue them, but you can use discretion to see if it is something you actually want to do, and if it is, I definitely recommend being in communication with your partner about it and checking in about how'd they feel about that.
I wonder, too, if you can start changing your language when it comes to how your relationships (either this one, or future ones) "end" - maybe instead of thinking "this is the beginning of the end," or "it's inevitable that we'll break up," you could start thinking, "I'm feeling a transformation starting to come on in this relationship," or "I wonder what's going to happen as we grow and change as people and as partners!" This small shift in thinking can help to un-demonize change in a relationship. Everybody changes, and lots of times, relatinships transform too as a result of this individual transformation.
Any death or loss is also an opportunity for a birth and renewal. When one thing exits our life, you can remember that it's inevitable that something new will come in to fill that void, even if you can't imagine it yet. Transformation or endings can feel painful, certainly, but if you can approach them with curiosity and neutrality instead of dread, you may feel better equipped to endure change and even find it interesting or exciting instead of the Bad Thing that we associate with "breaking up". Do you feel like you could try that out?