Harry is quite immature and enjoys annoying Nick and Charlie, as shown in Heartstopper (and the non-canon story Five Days of Solitaire). However, he will become more mature and supportive of Narlie's relationship later on Nick and Charlie, though, this is debatably due to his eagerness to gain popularity, as he only becomes this supportive of the relationship once others do, as pointed out by Oseman on her Tumblr page, which indicates that he's jumping on whatever is popular.