Multi-family house without spouse involvement - ownership question

That is a luxury problem... (word five...)

Unfortunately, often not. Then it comes to a forced sale.

Unfortunately, often not. Then it comes to forced auction.

A forced auction is not necessary. It is not necessary - his house, his decision to sell, to mortgage, or whatever to do with it.

ZV is not necessary. It is not necessary - his house, his decision to sell, to mortgage, or whatever to do with it.

If he can pay out the possible gain, of course that is no problem.

However, the loan must also be deducted from the accrued gains. So if the valuation is at least the same and payments have been made diligently, it should theoretically be exactly the asset increase that is newly eligible for lending. Since the life-sharing person is entitled to only half of the accrued gains, there should actually never be a problem paying this out, or am I missing something? If the market collapses, there are no accrued gains...

Let's see how the OP sees it. He doesn't answer anymore anyway.

An example: house is worth 800k. Divorce: no debts on the house. The woman is the owner and wants to keep the house. Ergo 400k gain. Now she has an income of 1000 euros. Husband 1500 euros. With that income the woman surely can’t get a loan.

That is not an example.
An example is: Man and woman have neither assets nor debts as a starting point. Woman builds house for 800k (of which 250k is gifted money like in the OP, the rest is loan). At the time of divorce it is still worth 800k. At that time both partners still have no other assets or debts. Thus gain is 250k (+ repayment from loan). Of that the man is entitled to 125k (+ half of the loan repayment). With the income of 1,000€ and the house as collateral she gets many loans. Even if the house is then worth a million, the man only gets 250k.
If she had not built the house but only put the 250k (which the OP also has) into the bank account, by the way she would still have to give 125k of that.

However, if the real estate boom comes to an end and the 800k house is worth only 600k at the time of divorce, the woman only has a gain of 50k (+ loan repayment), which she would have to share.