Purchase land + build a single-family house - not married

Form a GbR. This is registered in the land register with both partners as shareholders. The shares in the GbR can then be adjusted in the partnership agreement without any changes in the land register (and thus without additional notary and land register fees). The partnership agreement can also regulate what happens if one wants to exit (sell) or in the event of death (inheritance). Keyword pre-emption right.

The question was originally about the division of shares, but it would be more interesting and important to clarify how the partnership can be forcibly dissolved in the event of a separation. Because point 1 and 2 don’t help at all,

1) A partnership agreement in which the total costs and the funds contributed by each party are recorded?
2) Partnership agreement then notarized?

if one party cannot or does not want to pay out. The compulsory sale up to a forced auction would be important if no agreement can be reached.

Completely hypothetical, the following could happen:
- He pays 2/3, she pays 1/3. Corresponding ownership shares.
- Two or three children arrive, one of them an infant at the following event
- The man finds a new lover, to whom he moves.
So, but what happens now with the house? Must the woman pay out and reward the man’s lifestyle with €333,333? No idea how much money you really still have in reserve, but classically the house would have to be sold at this point. If the woman simply doesn’t want to do that, it will be a very lengthy process. No idea if this can be contractually regulated so easily, but putting a mother with children out on the street would be a hardship case that won’t happen quickly.

How binding are contracts that prescribe a compulsory sale after separation? Does that work in practice?