Yes it is your place. You deserve to be in an open and honest relationship. He didn't tell you in advance, which is really not fair. He should've told you, and given you the option to come too. After all, as a g/f who cares, I bet you would've liked to have been by your b/f side at this sad time to support him.

Personally I would tell him how this made you feel. Don't accuse or yell at him, but just say how you felt.

hugs to you...