I'm not happy this friend wants to tag along to an event with me.
Really? Why don't you want this friend of yours to come with you?
I just want to live my life on my own.
You shouldn't exclude someone that you call a friend. You are friends with them for a reason. If you no longer enjoy their company you should think about finding new friends.
That's not a valid reason.
While it is nice to include friends in your outings, you are right; you don't need to invite friends with you wherever you go. In fact, it is healthy to be able to enjoy your own company alone sometimes.If you want to do things on your own from time to time, you should, just make sure you aren't always excluding your friends.