Two self directed ira investors investing in each other?

[Sean H.]

I know with self directed iras, you are excluded from investing into family members. So, my girlfriend (no legal ties, other than the same address) has a lot of money in her self directed ira, and i will as well. If we each bought investment properties, could we each invest into each other's properties, so the opposite party whose money is invested into can freely spend their own money on the property?

*I already know you cannot mix your own money with your self directed ira money (hence why i came to this idea), and i know the stipulations about the loan having to have a set return (not a cut of the profit).