Luke: Lukey would probably be so wrapped up in work that he would forget your anniversary and as soon as he came home and saw you in your new dress with you hair done and everything he would feel horrible. You'd probably be mad at him (because hey he forgot your anniversary) and stomp to your room and he would come running after you to find you sitting up on your bed against the wall with your arms crossed and your heels kicked off. He'd say something like "(Y/N) I'm so sorry I was just wrapped with work and everything, I know that's no excuse to forget our anniversary and I'm really sorry" he'd continue sitting down next to you to try and get your eyes to look at his. "You look great by the way" he'd smirk earning a smile which would make him feel 1000× better. He'd then probably cuddle with you for the rest of the night saying how much of a dick he was for forgetting and he'd make sure to take the next day off no matter what it took so he could spend it with you and he'd buy you a really cute necklace and take you out to lunch and go to the beach or the park and have a fun day together and he'd spend the day showering you with kisses on the cheek bc he would be so thankful that you forgave him and that you understood that his work could be stressful and he'd promise not to ever forget your anniversary again.
Michael: I personally think Michael would be a bit similar to Luke in this situation bECAUSE MIKEY IS SUCH A KITTEN. Except I can picture him having a very relaxed day playing some video games and just chilling out then you would come home from work or whatever and talk about how excited you were for a reservation you made at a really fancy restaurant then he would be a bit confused and say something like "Woah what's the special occasion babe?" casually and then your heart would immediately sink and he could see it in your face and then it would all come back to him and be like "Oh god it's today? I'm so sorry I didn't" he could tell you were really disappointed and he hated seeing you down so he would quickly pick himself up and say "Come on let's go" you wouldn't know how to respond because Michael was the type to plan out occasions but he'd do anything to make you happy again. Knowing him he would rather just relax and cuddle while maybe putting on a movie of sorts. So that's exactly what you would suggest, you could tell he was in a good mood from just taking a break for the whole day so why not continue that and just snuggle together in your PJs? He'd be a bit hesitant at first and say "Are you sure? I mean we can still go to the restaurant I know you booked it and everything." You'd cut him off and reply with something like "Hey we can always go some other time, let's just cuddle for the rest of the night" He'd happily agree and attack you with hugs for the rest of the night while watching your favorite movies.
Ashton: Ohhhh Ashton, you and I both know Ashton is more active on twitter and social media than the rest of the boys. So he would have just woken up with you still in his arms. He'd then sit up while your still asleep next to him and open his twitter only to see his mentions filled with "Happy anniversary Ashton and (Y/N)!" and even the hashtag "#HappyAnniversary(Y/S/N)" trending world wide. Ashton would immediately go into a panic and be like "oh shit" he'd quickly get out of bed still trying not to wake you and cook up something for a breakfast in bed. While doing this he'd feel so guilty because he had a year to plan this but he only remembers that fREAKIN MORNING anyway he wouldn't want to lie and be like "Yeah I totally remembered that's why I only made you breakfast in bed". So once you woke up he'd say "sorry baby I forgot, I know I shouldn't have but I made you your favorite breakfast" he'd nervously smile and how could you not forgive him. You'd then spend the day just goofing around and ordering some takeout
Calum: I feel like Calum would just be going on with his day with you but you were clearly acting weird and ignoring him a bit. Calum would be clueless and finally he would ask "What's wrong babe?" Then you'd probably snap back and start telling him that it was your anniversary and he forgot all about it, immediately blood would rush to his cheeks "Aww I'm sorry (Y/N)" He'd try and win you over with the puppy face and holding his arms put to hug you but that wouldn't cut it. When Calum realized this wouldn't work he'd try another tactic "You know that fancy restaurant you like?"
"Yes I know that fancy restaurant I like" you'd shoot back
"Lets go there!"
"Calum we can't just GO there, you have to make reservations"
"I'm sure I can make some arrangements" he'd grin