Well, first off, the situation that happened between your friend and he is wrong. It shouldn't have happened, and I think it should underline an important thing to remember: He trusts you, not your friend. He also overreacted, but I'll get to that later.
He's decided that you are important enough to invest emotion, time, and effort. You are in his "circle", which to many guys is a very sacred(?) place to be. Your friend is none of those things to him. Even if you trust your friend to not tell other people about what you tell her, your boyfriend does not (nor should be be expected to).
Imagine this: You're at a party with your boyfriend. You and he are chatting with a guy friend of his. Suddenly, his friend says "oh man, chattycathythrowaway, that naked picture of you with your hair done up was so hot!" Suddenly, this person you aren't dating, nor have any intention of dating, has let you know that they have seen a very intimate side of you. It's likely something you never wanted them to know, and now your bf has shown it to them. What if he says "oh, but babe, I just really wanted his opinion on if you shaved your nether regions the right way!"?
Obviously it's an extreme comparison of the situation, but hopefully you understand my point. Guys, as a rule, are much less open about our emotions. By extension, our emotional stuff is much more private.
Now, I'm not suggesting you stop asking for advice from your friend. What I'd suggest, is to very much tone down the details, and if possible, maybe even change details in the future. It's not your boyfriend you're talking about, it's your other friend, Bill who's having _____ problem with his girlfriend, and you're not sure what advice to give. Something like that.
Now, onto your boyfriend's overreaction: From what you mentioned, the topic was innocent, and unless he gave you some reason why it should have remained private, he's gotta calm down. Maybe he feels like "if she told her friend that, what else has she told her?".
Communicate to him exactly what kind of stuff you feel is appropriate to talk to your friend about, and have a talk to compromise some things if he feels strongly about a couple (might make him feel like you care about his feelings).
As for working on his communication, here are some tricks I used when I had similar issues:
Whenever something annoyed me, I would take a deep breath, think out a complete sentence on why it bothered me, and I would voice my concern. In return, my gf agreed that she would hear out any of my concerns, even the silly ones (for the sake of getting me used to talking about it).
I would do reversal excercises in my head. If I felt wronged, I would flip the sides, and see how I would feel being blamed for what my gf had done. It's a good way to move past the anger, and find a solution.
Probably don't need this one, but we banned swear words during arguments. It's a lot easier to hear someone's problem out when it doesn't start with "You fucking...".
Hope you found at least something I wrote useful. Good luck working on the communication!