Maybe if your boyfriend and your mother know how you are feeling they won't take your words to heart. Tell them that you need to see your therapist you are just trying to hold things together until she gets back.
Go ahead and try to plan your birthday. Get your bf to help you choose music and activities. Do what you've seen other people your age do. As long as there is music and good food most people find things to do on their own. Give really good food.
Don't worry about being so social right now. Keep in touch enough so they don't forget about you but just do what you are comfortable with
Hold on until your therapist returns. Remember that she is able to help feel good and focus on that.
I hope you feel better soon.