Alliance Question

I am new to CC and was playing a game on Iberia earlier when someone was getting quite strong (player A), so I allied with someone (player B). Throughout the game I used a lot of my resource to keep player A from collecting 2-3 region bonuses per turn while player B, my ally, slowly grew very strong himself. At this point in the game I had a decent sized army but did not have any region bonuses. While my so called ally took a few of my 1 army spots, claiming that it is ok to since " I am just grabbing them for cards". At this point he took one of my 1 army spots and got the largest bonus on the map (8 armies). So in order to not allow him to become so strong to the point that he would easily win the game, I broke the bonus. At this point he freaked out saying I was a "fucking backstabber" and told me thats not how we do things here. So in that situation I am supposed to just allow him to collect a stupid amount of bonuses and basically let him win the game? If thats the case, then I think it is totally ridiculous.