Quote Originally Posted by underthesun
I had the pleasure of fighting just a few Helvetii Gaesatae. Damn, I need to get me some of those! :o
Told ya

How reliable are allies, usually, in EB? Any different than in vanilla?
Unfortunately, not much. It's a bit better, especially if you make regular gifts. If your income can't support that habit, you can give attacks on eleutheroi the turn before you'd be attacking them anyway.

Question 2: What factors affect your Allies' loyalty? I've never been able to figure out exactly why allies sometimes betray you.
Lots of factors in the diplomatic stance. Campaign difficulty above M gives a per turn penalty, so make friends early and often. Sharing a border makes them not like you, so Casse is your best bet long term. Gifts are often welcome, but sometimes not, for obscure reasons. Diplomatic trades on their terms instead of haggling. Etc.
Unfortunately, that's the diplomatic stance. Military movements are the way wars start, and the military AI literally doesn't talk to the diplomatic one, CA has said as much. So, you need to keep strong enough garrisons in your border cities that any attack would be repulsed, yet weak enough armies in border regions so as to not appear threatening. This statement does not imply that a level of force can always or even often be found that meets both criteria. Basically, sooner or later, if you share a land border, they'll come for you. Usually when you can least afford it. That's the fun part