I don't want to go to my friend's birthday party
Why don't you want to attend your friend's birthday party?
Because I'm not a party type of person!
You should always try to attend your friend's birthday party. Just go for a little while and make an appearance. They could feel hurt if you don't show.
I don't have time to attend every party. I have my own life to live.
If you get invited to an event you are expected to show up. If you really can't make it you can send a little goodwill gesture and call them or text.