Well I imagine Louis not letting it show unless he wants Harry to know.
So when Louis is upset he looks for Harry and just curls into him. Harry could be on the couch and Louis just plops down onto him, knees on either side of Harry and buries his tiny little hands in Harry’s shirt and lets his face fall to the crook of Harry’s neck because the smell of Harry always calms him down and Harry just kisses his head.
Or Harry is making tea and Louis comes up behind him and Harry is just like, “Oh Lou,” and he picks Louis up and puts him on the counter, hugging Louis close, he whole time asking “What’s wrong, baby?” and making sure Louis is okay and making Louis’ tea extra sweet.
Or Harry is in the shower and Louis just needs Harry so badly. Just needs for Harry to hold him so he gets in with Harry and Harry washes his hair and massages his back, whispering, “I love you,” after every time he kisses the places his fingers just were.
And Louis is all warm and cuddly in his pj’s and Harry makes him a warm tea and Louis falls asleep to Harry’s words of, “I love you” and “You’re okay,” and “I will make you chocolate chip pancakes in the morning” with the television playing in the background. So harry picks Louis up like a baby, Louis’ legs around him and he tucks Louis into bed before cuddling into Louis, making sure Louis knows he’s loved.