An apology wouldnt go back and change things. Its just accepting responsibilty for your actions. You had plans with him, and you cancelled them for something better, inconveniencing him. I understand perfectly.

Hes saying you have your priorities wrong. Why does your boyfriend coming in and reminding you later that its your anniversary, take precedence over your friends plan to stay with you? You didnt even realize it was your anniversary until bf said so. You hurt his feelings. An apology doesnt cost you anything, but not offering one may cost you this friendship.

Just explain you were squeezed between a rock and a hard place, and you took the easy way out for you, but the hard way out for him. And youre sorry.