Hi. Some quick, important things.
First, my native language isn't english, so please forgive my mistakes, I tried my best.
Second I hope you'll like it. :)

"Your hand fits in mine like its made just for me"
Louis is at home. He misses Harry, but he missed his family too, and he's happy that he can be home for the weekend. But his mind keep wandering back to Harry, and how much he loves him. How much he loves to hold his hand. And he can't wait for the time when they can do it in public, because they're holding hands all the time. When one of them is sad, or happy. When they're hanging with the boys. When they're on the couch at their home, when they're kissing, when they're making love, when they're asleep they're holding hands. And Louis loves it, and he thinks that Harry's hand fits in his hand, like his T-shirt fits on him. And he smiles at the thought.

"But bear this in mind it was meant to be"
Harry didn't belive in soul mates, in fate, in destiny or whatever. He didn't think that this kind of sloppy bullshit is real. But oh boy, he was wrong. When he found out that Louis and him were at the same concert, in the same gig, he was suprised. Because that couldn't be an accident. The universe had a plan for them, but when Louis and him seperately decided after the concert, that they wanna do this for the rest of their lifes, the universe let them go, cause it had a bigger plan for them, and it put them together in a band with three others. Harry can't help, but thinks that Louis and him are meant to be.

"And I'm joining up the dots with the freckles on your cheeks"
When you stand close enough to Louis you can see the tiny freckles on his cheek. They're little and Louis isn't sure if he likes them, but that's okay, cause Harry loves them instead of him.

"And it all makes sense to me"
It's a little hard for Louis to put into words how much he loves Harry. Because he feels like with this feeling he has all the knowledge, and with this feeling every cheesy love story and love song make sense, cause he's feeling the same way.

"I know you've never loved the wrinkles by your eyes when you smile"
When Louis is smiling for real the whole world stops and stands for a while because it's so damn beautiful. When Louis smile reaches his eyes it makes little wrinkles around them, and the corner of his mouth is reaching up, and Louis is a little ball of sunshine. And when he smiles like that Harry falls in love with him again.

"You've never loved your stomach or your thighs, the dimples in your back at the bottom of your spine, but I love them endlessly"
Sometimes Louis wants to disappear, because he doesn't feel good about his body. He doesn't love a lot of things about himself, but he never mentions it, because he doesn't want to sound like a precarious teenage girl. And in these times he doesn't understand why Harry wants him, because he can get so much better than Louis. But Harry, as the perfect boyfriend he is, he always notices when Louis feels this way. And when he does, Harry makes sure to let Louis know that he is perfect, that he loves him, that he turns him on, he lets Louis know this by secret touches, stolen kisses, because Harry would never change a thing about him, and he never trade Louis for anything.

"And I won't let these little things slip out of my mouth, but if I do, it's you, oh it's you and they add up to, and I'm in love with you, and all your little things"

"You can't go to bed without a cup of tea"
When Harry is sad, or homesick, or feeling alone, Louis tries his best to cheer him up. He tells him jokes, he watch Love Actually with him for the millionth time, and before bed time, Louis makes tea for Harry, because once Harry told him that he makes the best tea in the world, and his tea tastes like home, so when Louis has a chance he does this for Harry.

"And maybe that's the reason that you talk in your sleep and all these converstations are the secrets that I keep"
The first time Louis hears Harry talks in his sleep he was half asleep. He thought that Harry was awake and he asked him what did he said but the answer was silence. He didn't understand but he didn't care because he was way too sleepy. But at the edge of the sleep he heard Harry spoke again, and this time he sat up, and looked at Harry to ask him repeat what he said. And that was the moment when he realized that his love was asleep. He just stared at him in awe, and hoped the he would say something more. And he did actually. He said Louis' name and after that turned to his other side and mumbled something else and Louis' heart swelled with emotions. He loved Harry even more even thought he didn't think that's possible. And he's never mentoined it to Harry or anyone else, because that is his secret, and he always hopes that Harry will talk in his sleep every night.

"Though it makes no sense to me"
Sometimes Harry doesn't understand that how is it possible to love someone like he loves Louis. Harry loves him with everything he has. He loves him so much, sometimes it hurts. And sometimes all he want to do is hug him tightly and never let him go. Because he's afraid if he lets him go he will disappear in the distance and never comes back. That's why he gets jealous sometimes. He can't help it. He's jelaous that anyone can touch him, hug him, cuddle with him in public but not Harry. He knows why, but that doesn't mean he doesn't want to. He loves Louis like he never loved anyone, and it doesn't make sense, because love doesn't make sense. But that's okay, because he loves Louis.

"I know you've never loved the sound of your voice on tape"
Sometimes Louis doesn't understand what the heck he is doing in the world's biggest boyband. He isn't good-looking enough, his isn't nice enough, his voice isn't strong enough, he just... isn't enough. And he hates this. He's trying not to feel this way, but he can't help himself, because he knows deep down that this is the truth. When he feels this way he always comes to Harry and cuddle with him, but now it's different, because he just... He can't explain it, but he just can't go to Harry and mumble about his self pity again. He has to act like a grownup for god's sake. Afterall he is the oldest member, he can solve his problem by himself.
But the best thing is, Louis doesn't have to go to Harry, because he notices Louis mood without a word, and he is by his side, like always, and he comforts him, like always.

"You've never want to know how much your weight you still have to squeeze into your jeans but you're perfect to me"
The truth is that Louis has his dark moments but Harry has them too. He's always wanted to be that person who don't give a shit about other's opinions, he's always wanted to live his life without regrets, but he is a human after all, so he has his dark moments. He hates the dating rumors, he hates that he can't be who he wanna be, annd sometimes he hates how he is looking. He trying to be half as strong as Louis, but he always fails, and he hates that. In fact, he hates everything.
And as much as Harry notices when Louis is in a bad mood, Louis notices Harry's bad mood too. And he always there to cheer him up, to comfort him, to love him, whenever Harry needs him. And after some kisses and cuddles and kind words Harry doesn't hate everything because Louis finds him perfect, and that is more than enough for Harry.

"I won't let these little things slip out of my mouth but if it's true it's you, it's you they add up to I'm in love with you and all these little things"

"You'll never love yourself half as much as I love you"
Harry knows that despite his dark moments Louis loves himself and his life. But he is sure that no one will ever love Louis as much as Harry loves him and that involves Louis too.
And Louis feels the same about Harry.

"And you never treat yourself right darling but I want you to"
Louis is the best person in Harry's opinion. Harry never met with someone who was as funny, as lovely, as caring as Louis. Louis holds some people close to his heart, and they're the luckiest. Because if Louis loves someone he always makes sure to let them know that. He calls his mother everyday, he speaks with his sisters too, he always has a nice word for every lad, and he even treat Eleanor with respect despite the fact that he doesn't love her. So Harry just doesn't understand why Louis can't treat himself right.

"And I let you know that I'm here for you"
Back in the old times, Harry really missed his mom and his sister too, when he was at the X Factor house. He felt really sick, homesick, and he would give anything for one hour with his loved ones. But he couldn't do that, so he just sat on his bed and he tried his hardest to not to cry. He never missed his family this much, and it became harder with every minute. And suddenly the door opened and Louis stepped in, because he felt that there was something with his best lad so he just came and sat with Harry, and waited till Harry couldn't hold it in, and told Louis what was his problem. Louis was there for Harry back then, he is there for Harry now, and he will be there for Harry the rest of his life.

"And maybe you'll love yourself like I love you"
Harry has a nice smile for everyone. Even for strangers and paparazzis. He's never been rude or impolite to anyone. Ha can love anybody without conditions. This is his nature. Sometimes Louis doesn't know how Harry manages to be nice for everyone when he is clearly not in the mood for people. Harry always smiles, always loves, he is just a happy person and easy to get along with him. And Louis doesn't know how Harry can't see that. It's not like Harry hates himself because it isn't true, he just happen to think that he is average. And in Louis' opinion this is not the case. Because Harry is everything but average.

"And I've just let these little things slip out of my mout 'cause it's you, oh, it's you, it's you they add up to and I'm in love with you and all these little things

I won't let these little things slip out of my mouth but if it's true it's you,iIt's you they add up to I'm in love with you and all your little things"