Hhmm doesn’t sound much of a friend. You financially supported her (hundreds of thousands of dollars??? Say what….) while she slept with other men (are you romantically into her?) and then she just ghosted you.

Now having said that, you can’t control other people or get answers why people do what they do. You can only control yourself. I’d get to the bottom of what makes you want to spend exuberant amount of money on other people? I suggest therapy