House purchase - split the price 50/50

Land registry is land registry and financing is financing. Two different things. It goes 50/50 into the land registry and finances the loan together. Your wife provides equity, you do not, and that should be regulated by a private contract, e.g. through a private loan. She can give you an interest-free loan for half of her equity, which is to be repaid by you in case of separation. Then, each of you normally pays off half of the bank loan. You should think about the worst-case scenario beforehand. What if... who takes over the house or who can and wants to at all. That can be settled fairly. But everything should actually be regulated according to the above option.

First of all, you should ask the neighbor if she actually wants to sell. Maybe she doesn't even know about her moving plans herself.

Well, I already have her statement that they want to sell in 2020. So we still have some time to agree on the financial aspects. I found out that they paid 90,000 DM for half back then (2000). Afterwards, they did quite a bit, probably doubling the living space by converting the attic. I'm really curious what price they will ask for.

My current favorite would be financing with both names included, she contributes her share as equity and I pay the loan.
So, many thanks for the suggestions already, they have helped me a lot.

hm I had my half from equity and the other half is "his" loan, which we both signed together. Since I can't afford the house alone anyway in case of a separation, that's okay.

But unfortunately that also means if he moves out and stops paying the loan, the bank will come to you and want its money.

But unfortunately that also means if he moves out and stops servicing the loan, the bank will come to you and want their money

I was and am aware of that

The real crucial question is whether one tends to think more in terms of opportunities or risks. Both attitudes have their justification and both have their own pitfalls. From this arise the preferences for a joint financing. The risk observer tends to find the opportunity thinker "romantic-naive-naïve." The opportunity thinker tends to find the risk thinker "dry-cynical-pessimistic." The very clever ones define their own thinking as "rational" – and that in a completely irrational negation of the limited scope of their horizon. What should I advise you as an unwavering optimist and "opportunity thinker"?

You write in the original post that she is your "wife." So you are married? Then why a separation of the funds for the house?