Paying "rent" to the partner... how?

... because I've already set my sights on a new STIHL...

The main thing is, don't look at it too lovingly. For my husband and me, it's now a running gag when we're at the hardware store. In front of the STIHL, I always say to him, "hey, don't look so in love."

Thank you I at least feel a little understood

I know that he and I think similarly in this regard and we both approach it with a lot/too much head. But on the other hand, we don't resent each other for viewing living together as unromantic/calculating/considering all eventualities/shaped by experience. If this is called a utilitarian community here, then so be it.

A single joint account can work for some, but it won’t work for us. Still, I don’t want to keep track of the €18.70 at Aldi, so a joint account for living expenses.

And in the hardware store we also stand together in front of the tools and look quite lovingly first at the little machine and then even at each other, even in our utilitarian community.

you want to secure yourself, which is legitimate. I also think it’s good that you are thinking about it. Once clarified and put on paper, life becomes much easier. Nevertheless, you have to see the whole picture. We don’t have a joint account either. We don’t need one. Just a household cash fund. Most of the money comes from me. Vacations are also mostly financed by me. She gives as much as she can/wants. My wife has a secure income, is still paying off a property (rented out), and is preparing for retirement. Additionally, as already mentioned, she is contractually secured through me. We would never think of settling accounts over a few euros (for example, shopping at Aldi). But we are also in the fortunate position of not having to count every cent twice. To be able to stay in the property (even just temporarily) you either have to have a share in it or a right of residence. An official rental model is certainly not very sensible as it is taxed. If you get married it will be easier since there could then be maintenance, etc. Then there’s the question of separation of property or community of accrued gains...

We do it like this: We moved in together when she was doing her FSJ. I paid the majority of the rent since she only had part-time jobs. Nevertheless, she insisted on paying a share. After completing the childcare training following the FSJ and starting working life, we obviously went 50-50.

Now we live in the house that I financed alone and in whose land register I am the sole owner.

She still pays the 50% of the rent that she already paid in the rental apartment. So from building the house's perspective, she has no disadvantages but lives significantly better for the same amount of money.

I find nordanney’s suggestion very appropriate. I calculated it for us once, and we actually end up in the proposed range.

We have an extra joint account for groceries etc. into which we both pay 50-50.

It’s working great for us so far.

I would never officially charge rent. Feels weird and I’m not going to pay taxes for such nonsense. They already get more than enough taxes from me. Transfer to my account and that’s it.

Does not guarantee that you can put them out on the street. And that was important to the OP. I like your solution.

It just doesn't guarantee that you can kick them out on the street. And that was important to the OP. I think your solution is good.

It is basically secured through the payment of the "operating cost share" (or whatever it is called) as soon as this is higher than 50% of the actual operating costs. In the worst case, any judge would probably interpret this as hidden rent payment and grant corresponding tenant rights. For the landlord as the "evictor," there is also the risk of being accused of tax evasion. Hopefully, that is enough time even in crisis situations to be able to spend time in the guest room until moving into the new own apartment.