I don't know Civ, but for practising the kind of strategizing you're describing I'd recommend Neptune's Pride.

and I've known people for whom the opposite was tragically true.

Heh. I'm one of those people. I practically fell in love with my first ally. I'm lucky they were really nice when they broke my lines, essentially throwing me a sword and telling me to defend myself before starting the invasion. I'd have been heartbroken otherwise. I guess to an extent I thought they were damning us both to death by zombie bot rush by breaking our alliance, but their judgement was apt, after crippling me they proceeded to conquer the galaxy, barely worse for wear.

It was from this game that I learned the reason I have an intermittent habit of falling head over heels in love with friends probably has more to do with diplomacy than anything else. I can rapidly build unreasonably strong alliances from nothing this way, at the cost of forming a few confusing, inconvenient bonds when I hit the wrong target. It's always nice to learn that the quirks of your mechanism serve a purpose.