My father [M55] lied about something crucial (at least to me) to his girlfriend [F45]

My mother passed away five years ago. Since then my father got over depression and got himself a new girlfriend.
Now the problem: I randomly learnt (his girlfriend mentioned in a text message "that house you used to have") that he lied to her that he had to sell off a vacation house WE NEVER HAD to pay for my mother's medical bills WHICH SHE DID NOT HAVE because of the medical insurance. Now this is something completely out of character of him to do; I was completely baffled when I learned about it.
I am sure we never had it, because... why would they both hide something like that from their children? and the house would have been in a foreign land - and the trips thereto would be really hard to miss... that's why I am quite sure it's not true.
One possible reason I can think of that my father is a struggling entrepreneur and super self conscious of not making as much money as he hoped he would and this whole lies must have been a show off attempt gone terribly wrong.
The thing that bothers me so much that my mother would never ever agree to something like that! She was pretty adamant of not getting our family into financial trouble because of the illness, that's why she opted for the cheaper (but still good quality) government healthcare insurance. Telling stories like that completely distorts her image and pisses me off to no end.
Another reason though... guilt. What if we did sell off the real estate we did have and paid for the more expensive treatment? Would she still be alive? Did we all try hard enough? Maybe he is making stories to make him feel better - like we did everything we could.
How to confront? Should I confront him or should I just let it go? I learnt about that yesterday and decided to cool off first..
UPD1: Double-checked all the family property-related documents, tax filings, my mum's old e-mails, my older brother. Nah. Not there.
UPD2: On why it is so important to me: Medical bills are not degrading, of course not. But she sacrificed not to spend $$$ on the additional medical services. I offered my college savings, she declined. We offered to sell the apartment, she declined. Hell knows, might have been better in Israel or somewhere else, but she did not want to take the family's money for what she believed to be lost case. And yes, that keeps me up at night, thinking about "what-if-we-insisted". And then I hear this...
TL:DR: father made up some stupid lies about imaginary house he had to sell off to pay for my late mothers' medical bills


Source.