I get into this situation a lot of the time.

AI: We want to end this deal now.

I renegotiate the deal, sometimes offering up an arm and a leg. Later, that AI declares WAR on me. This is just bad. Are they declaring war just to cancel a renegotiated deal?!

maybe they hate you. maybe that's why they canceled the deal. maybe another civ negotiated a trade embargo, followed by a war request.

The first time it happened, a pleased Shi Huangdi backstabbed me.

The second time it happened, Cyrus backstabbed me just after I voted for him in an AP election. So they don't "hate" me.

I think it's just a weird side-effect of the diplomacy system. Sometimes, AI leaders will act bizarrely, because they are controlled by random numbers. Maybe someone will vote for you, then declare war the very next turn. Maybe someone will ask you for a resource deal, then declare war the very next turn. Their behavior isn't always sane.

One thing you could do is force peace for ten turns whenever a resource deal is made. Obviously, this can be exploited in a major way. However, if you're not going to exploit it, and it makes the game less random/bizarre/unrealistic for you, then I don't see any reason why you couldn't mod it in. However, I'm pretty sure this would require use of the SDK, rather than python.

I think you might just not have enought troops. The AI leaders have different chances to backstab you - and Powerslave ^ is right about some randomness playing into it. However this will not happen if you have some power. You not need to be the most powerfull Civ around, just reasonable powerfull.