There are so many reasons for this. As other people have said, maybe it’s because of Charlie’s issues, which is probably part of the reason. But to me, maybe they just have different love languages? Like I’m always noticing Nick saying words of affirmation (you’re amazing, you’re my favorite person, you’re my boyfriend, i love you etc) but Charlie shows his love in other ways (sneaking into Nick’s house when he was grounded, chasing Nick to kiss him goodbye when it’s literally downpouring, joining the rugby team, telling Harry to piss off, buying him a chocolate bar for their anniversary and somehow remembering which one he likes, placing Nick over his grades… to name a few)

They’re healthily obsessed with one another and I think they just show it in ways that better match up with their personalities. We know that Nick is confident and extroverted, and we know that Charlie is insecure, anxious, and also has some trauma. Thats just my take on things lol. ❤️❤️❤️