Why do I enjoy the idea of hanging out with people, but I don't actually enjoy actually hanging out with people?
I can tell you exactly why "I" do this. I am a Romantic. Always have been, always will be. So, the idea of hanging out with people sometimes seems like an awesome thing to do. Then i think about what actually happens when i do and how rare is it truly a wondrous experience. Sure, i recall some of the best moments in my life and they have often been with other people. But, for every one of those special moments, there are perhaps a thousand times it fucking sucked. Each of the great times was spontaneous and the person or people i was with were or are extraordinary. They are head and shoulders above the average person out there.
So, even though i sometimes do have a rememberable visit, they are rare. Even with the few people that i love and value the most. I need to be in the right frame of mind and they need to be in a similar state. How often do the stars align? Learn to entertain yourself, but do try to be a good friend to those you do care about. Be honest with them, and yourself about when you actually can and want to be with them and when you simply are not up for it. If they are real friends, they'll understand that you often don't go out with them, and if and when you do, you may cut-out early because you are depleted and need to recharge.
My solution: be the introverted romantic you actually are. It is perfectly acceptable to want/need solitude.