The error is in spending thousands of dollars on a woman who is not your wife or mother.I am sure that is true. However, it strikes as fundamentally unjust that a woman can claim for every pair of trousers she has washed for a man but a man can not claim for a 7000 USD luxury holiday, an expensive gift he made, money paid in otherwise in the expectation that the woman would be faithful to him. However if she then leaves, unilaterally breaks the contract, should she not be financially accountable as well?
That seems only equitable and would in theory further underline a woman's need to be faithful in a world where 50% of marriages end in divorces, the vast majority initiated by women.
If you are expecting women to believe in a quid pro quo reciprocity for material things a man is offering her, you are expecting something that is unnatural and only makes sense from a male, logical brain, and not a feminine, emotional one. In other words, you could force her to pay you money back, but that will not make sense to her and she will not alter her behavior.
Outside of vacations, which were always places I wanted to go anyway, and only cost marginally more to bring a girlfriend along, I have never spent more than a few hundred dollars on women I have dated. I have a friend who just bought a $100+ dress for a girl on their 3rd date. If you want to go that route, don't expect to ever see that money again, and be aware you may be sending bad signals to the woman, encouraging gold diggers, and being seen as a simp.
Plus if she was getting $7,000 vacations as a girlfriend, what is she going to expect as your wife?