Well first I'm going to direct you to a couple of posts you should definitely check out:

junkshop_disco made this awesome 1D primer (http://junkshop-disco.livejournal.com/40473.html) that I just found last night and its fabulous.

Also if you have like, an entire week to waste, this tumblr (http://reasonswhylarrystylinsonisreal.tumblr.com/post/22345529322/reasons-why-larry-stylinson-is-real-masterpost) has like every single Harry/Louis moment ever recorded.

But basically they're all just super adorable and they can't seem to keep their hands off each other and its precious. Harry is 18 and he's the youngest, so they're all legal :)