Would differentiate the value increase depending on whether it is an inhabited single-family house built during the relationship or rented properties
Death and child/children is another issue. In my opinion, the legal regulations, whether married or not, are not sufficient.
Now it is about finding an arrangement that both can live with unmarried, married, separated, or divorced. Especially beforehand, reasonable arrangements can be made for the separation. When in a bitter dispute, the logical center in the brain is off.
Make an appointment with the notary who also handles the property contracts and have both of you advised.
They are knowledgeable in contract law, as long as nothing is signed, cheaper than a tax advisor (who is usually very tax-focused)
Possibly he can fit you in before the appointment.
And talk about how you imagine it.