He doesn’t have friends
You haven’t noticed because, you’ve only gotten the good side of that so far: he’s had tons of time to spend with you. But, eventually, you’ll get over the honeymoon phase and want to go out with your friends and do some things without him and…uh oh. He won’t like it. Because, you’re his world. Also, why doesn’t he have any friends? That’s something worth investigating. He may be untrustworthy and burnt a lot of bridges in his life.