This is not the moment to let them know you’re disappointed. If they do show up, then you should enjoy the celebration with them. Cut your cake and have a good time. However, you’ve been given a great opportunity to learn more about these friends. They’re not people who show up all the time, and without punishing them, just know this and act accordingly. For your next birthday, don’t include them in plans that are important to you. Sometimes friends are good at one thing and not another — they may be great if things are bad and you need support, but not so good at showing up for birthdays. Learning about each other and adjusting the relationship to this knowledge is how you can have successful relationships with imperfect people! 😉