That said, I am curious why you lend him 31.5 BTC (not a small amount) in the first place. The interest 0.5 BTC (less than 2%) is not so attractive in my opinion. Did he give you any collateral? I doubt you will just choose to trust him because the tiny trade before.
Read the logs. He convinced me that he was a good guy, and I tend to help people. Who knows me can confirm it. I don't want to abuse and earn on honest people, I didn't do it for business, I just did it as a favor. And I have been burnt. I am so disgusted, and I am angry with myself for trusting people too much.
Actually, I think Theymos does not need to make PMs public. He just need to confirm that the part you chose to disclose is genuine, and that will be enough.
To the future potential buyers of this 'Cloud Hashing' contract, be CAREFUL if something is too good to be true. Please stop risking your money before all these things are settled.