Paid for the kitchen in my girlfriend's rented apartment, relationship over

I've probably made one of the stupidest financial decisions of my life and I'm just trying to figure out if there's anything left to save. My girlfriend and I were together for almost 5 years. We had been talking about moving in together for a while. She had a relatively nice old apartment in a good location, but with a very old kitchen that was half falling apart. Since the apartment is cheap and we both actually wanted to stay there long-term,