The average rent for a one-bedroom apartment is between €300 and €400 at best; thus, I was thinking that taking a loan is as costly as paying rent per month, but after 15-20 years, you end up with a house. My main concerns are the following: First, if you're in a long-term relationship like myself, you can never be 100% sure that you'll be with that person in 20 or 30 years from now, which might prevent you from opting for a loan. Secondly, you need to be certain that the location or city of the property to be bought is convenient for future job offers and so on. Thirdly, because a loan is a many-year commitment, there's no guarantee that you'll be able to afford the monthly payment 15 years from now.
Mathematical calculations like that, friend, why not take out a loan to buy a place to live instead of having to spend money every month to pay rent. Isn't that what always crosses your mind?
If you want to take out a loan, what is the collateral? lenders (banks or other lending institutions will not simply disburse money without collateral). Borrowing money from moneylenders is not a good idea, especially in large amounts. It's like killing yourself because besides having to pay monthly installments, the interest is very high.
Wanting to have a private residence is a good idea, you should start from now by setting aside some money from your monthly income. Your concern about the three points above will increasingly make you trapped in a situation, you have to take a stand. As a man, you have an important role to play in providing a decent life for your spouse and children. Keep going, then take a stand after getting the best decision.