Your own insecurities is a you problem, you should work on that, if you can't, don't be with anyone because all you're going to do is hurt 2 people, one being yourself.

However, this is not that major, just say sorry, ask him why her smiling was important, ask if she is ok.. You might find out your boyfriend is just being supportive of a friend.

The only slight downside I guess is, you have been together for over a year, if his friend is going through something, usually your partner would share minor details at some point.