@Glomoro You miss the joke. Japan manga cafe isn't a place to meet girl since even though they are called cafe, they don't look like normal cafe at all. They are full of single-person cubicles where a person can read in private, you can even spend the night there.
His brother doesn't have any girlfriend. This happen in plenty of other manga and anime. A character said that he will spend Christmas with his girlfriend but it turns out, he is just at a manga cafe, reading manga for a whole day. Maruyama is just being considerate to his brother.