I for one found it frustrating when the AI that I was depending on for support in defending a key system is in fact allied with the AI that's attacking me.  I really think we should be able to know if certain sides are allies or not, short of observing how their ships behave towards each other.  I would love to know the full extent of each side's relationships with each other, as well as with me.  Of course, maybe you have to ask them, and maybe they'll turn down your request for transparency and open negotiations.  (Disinclined to acquiesce to your reqeust, as it were.)  Or maybe you can have spies and espionage to determine the state of that empire's alliances.  Maybe even have secret alliances where they act like enemies, but are secretly conspiring against you.  But really, we just need some way to know how the other sides feel about each other.