To try to keep it short, my father ended up in a ton of debt when he divorced my mom. 3 years later, he finally recovered and is in a better financial position than before, but now he wants to marry again.

This time, the female in question acts like a teenager with passive-aggressive behavior (no surprise there) and is also very protective of what she does on her phone. I was sitting next to her and whenever I looked in her direction, I couldn't help but noticed that she flinched and immediately closed the window twice, even though she was just on instagram looking at some girl's page. If she does this by reflex by now for something trivial, then she must be hiding some serious shit.

Furthermore, it's very obvious she isn't being genuine with my father. The tension that builds when some minor inconvenience happens is palpable, but my dad just can't see it.

How do I save him from marrying this girl and making a huge mistake?