Exclusive? No. If I had that kind of money, I would spend a good bit of it on my ATF, but I have no interest in stopping her from sleeping with anyone else she wants to, paid or not. I'd certainly spend more time with her. Perhaps make an arrangement where I get her an apartment and an allowance, in exchange for her blocking out time for me.
Putting aside the ATF question, let's assume I'm going to spend the entire $50M on sex. That's a budget of about $30k/wk for the rest of my life. Absolutely no end to what I could do. I'd probably have to hire an assistant to work out all the details, even tracking down all the UTR, retired, and untouchable pornstars I would love to bang.