Girlfriend And I Bought A House, What Should I Do After We Break Up?

Location: California
About 10 years ago my girlfriend and I bought a house together. We were never married and we couldn't qualify for a traditional loan. Her parents are rich, real estate investors, so they essentially loaned us the cash for a foreclosure which we purchased from the bank with the intent on fixing it up, for about $300k. It was in very rough shape.
Both she and I's names are on all the legal documents and it was purchased in our name.
Her mother set us up to pay a 20 year mortgage which I believe they acquired by refinancing on other properties they have in other states.

For the first few years, I paid the mortgage and all the bills. When the pandemic hit, I lost my job and started my own business. Her parents told me not to worry about paying the mortgage and just pay the bills. In years since, between girlfriend and I, we have put about $50K into the house fixing it up, and I've done most of the work myself, with girlfriend paying for most of the materials.

Girlfriend is a chronic traveler and spends about 75% of her time out of state. About a year ago, I found out she had been cheating on me (I have proof). I broke up with her, but I don't want to move out of the house and she's usually not here. She has 2 other homes out of state where she spends most of her time. I live here full time and have no other residence. We discussed selling the house, but she argues, since I haven't been making the mortgage payment for the last 5 years, I shouldn't be entitled to 50% of the profit. She claims she has been making the payments.

We still owe about $200k on the house to her family. The house, after our many improvements, is currently valued at about $600k. I cannot afford to buy her out, which I imagine would require paying off the original loan and at least half the difference, so a total of somewhere around $400k total. I've spoken with her parents and made them aware of what happened. They haven't made any solid statements about the matter.

What are my options? Try to get a bank loan to buy the house from them? Move out, sell and fight to get 50%? The real estate market where I am is currently in a downturn and I don't like the idea of giving up on this house I put so much effort into.