I hate to say it, but I don't think you need a €3000 computer.
$3000 is a gaming PC, or CAD PC. Unless you're a professional streamer or a CAD designer, you don't need it. You can get a decent computer for 1/2-1/3 of that price.
At the same time, it's okay to buy things you don't need, if you can afford them. But you have to decide if you should.
What I would do:
Talk with my partner to see what they think, as they might be also affected by my decision. I would re-think the budget for the PC as 3000 EUR is a considerable amount, I would try to compromise. But if I don't change my mind then I will plan accordingly.
I would then save "extra" when possible, so I pay the computer to myself.
The fear you feel is important to notice and accept. I'm glad that you're already doing that. I think it's equally important to notice and accept your impulse to get the €3,000 computer. What is your brain telling you?
After realizing that there's a part of you that is afraid of losing money, and there's another part of you telling you to go after the €3,000 computer, notice yet other part of you that simply notices. This other part of you simply observes. It helps you to take distance from your thoughts, emotions, impulses, memories, etc.
Now think about what you value. If you weren't limited by fear or impulses, how would you like to act? How would you like to be remembered. What do you stand for on your life?
Finally, think about what the next step towards that kind of life would be like.
Everything that you just heard is based on Acceptance and Commitment Therapy. You could search for Russ Harris or Steven Hayes for more information on it :) it could help you make a decision.
Good luck! :)
Will you use it for work? Can you write it off as a business expense? Those are the things I considered the last time I went a bit over budget on a new computer. I bought a professional grade laptop with a graphics card that could handle pretty robust design work and it was still less than half of what you are looking to spend so maybe you could get by with something less? But it sounds like you know what you want if it's worth it to you.