How can you see the marauders & Lily reacting to Regulus/Remus and how might this change if looked at from a multishipping perspective?
Before I begin, thanks for the question!Now onto the answer.
I actually found this a difficult questionto answer, not in the sense that I didnāt understand it, but that because ofhow little we know about the Marauders during the Marauder Era, there could bea multitude of different reactions. However, I have thought about Siriusāpossible reactions in the past so Iāll start there.
I see Sirius looking at this like abetrayal. Heās likely ranted to Remus (and the other Marauders) on a multitudeof occasions regarding Regulus ā how he stands on the side-lines when heāsfighting with their parents, how he follows along with the pureblood ideology,and just in general how opposite he is of Sirius. Sirius would say somethingrather stupid, probably using Remusā condition and its ādarkā nature againsthim or something else inflammatory. Remus would shut him down with anotherinsult, delivered with all the cool calmness Sirius associates with Slytherinthat would leave Sirius shouting āSlytherin wanna-beā at Remusā retreatingback. Ā Remus would leave Sirius to simmerand eventually Sirius would calm down enough to be civil but he still wouldnātunderstand why itās happening. Eventually heād come to accept it but heād stillbe pretty grossed out about it (āMoony, heās my brother and a Slytherin ā donātsnog him in front of me!ā).
This is of course, if Sirius found outabout during the course of Hogwarts. I personally donāt believe that wouldhappen; Remus and Regulus would keep their relationship a secret, Remus becausehe worries it might ruin his friendship with Sirius and that the otherMarauders would take Siriusā side and Regulus because it would ruin his imageas the good son and proper Black heir. This is not to say that I donāt thinkSirius never found out; I think that during Siriusā time spent at GrimmauldPlace in book 5, Remus confessed to the relationship. I also think that Siriuswould be accepting during this time because it happened in the past and thatthey wouldnāt really speak any more of it.
As for Lily, James, and Peter, I think theyādskip the outrage that Sirius has and skip straight to the confusion. After all,Regulus is the perfect pureblood prince; why is he in a relationship withRemus? And why is Remus in it? What does he see in it? Is Remus just in it becauseRegulus looks so much like Sirius?
I think at first, in public, James wouldnātspeak to Remus because Sirius is his brother and he has to stand by his brotherāsside, but behind the scenes he would still treat Remus as Moony. Remus wouldunderstand this as well and harbour no ill-will towards James for sticking bySirius ā Sirius is a rather delicate person even if he says he isnāt and wouldprobably be in a really bad place if James abandoned him. Still, Remus wouldrant about Sirius to James when they were alone and James would make subtlecomments about Remus and Regulusā relationship being okay to Sirius. Jamesprobably wouldnāt spend a lot of time around the couple before Sirius accepts itso heād be pretty confused for as long as Sirius is but eventually heād seethem and understand why theyāre drawn to one another.
For Peter, I have a feeling he would betorn between James and Sirius and Remus, leading him to spend one day withJames and Sirius and the next with Remus and Regulus. I think heād see a lotmore of Remus and Regulusā relationship, therefore seeing just how much theylove each other and that Regulus isnāt just a substitute for Sirius. As thefight wore on, I think heād end up showing more and more support for Remus andRegulus, eventually culminating in him telling Sirius that heās being āfuckingridiculousā and to āget over himself.ā
As for Lily, I donāt think sheād be veryprivy to the goings on of the Marauders when Remus and Regulus are firstrevealed (I believe their relationship starts when Remus is in fifth year andRegulus is in fourth year). Like the rest of the onlookers, sheād be confused,and perhaps sheād ask Remus why he was with Regulus during prefect patrols butfor the most part, it would be a rather insignificant deal in her mind. Inseventh year, when she becomes more āinā with the group, sheād see that Remusand Regulus do truly love each other even though at the point theirrelationship would be sailing into rougher seas with the Black familypressuring Regulus to be the perfect heir, to get engaged to a perfectpureblood wife and to take the Dark Mark.
As for from a multishipping POV, Iām goingto look at it from a Wolfstar (Remus x Sirius) POV since I also ship that one.
Most of the reactions would be the same,but the reasoning would be different. The main reason people would be confusedabout their relationship and what most people would think at first, is thatRemus is only with Regulus as a stand-in for Sirius. Sirius would be upsetbecause he loves Remus. I have a feeling that in this scenario, Sirius wouldhave confessed his feelings to Remus, been rejected, and then when he pushesfor more information, been told Remus was already with Regulus so there wouldalso be some feelings like Regulus stole Remus from Sirius thrown in. Also, ifwe throw in to the scenario that eventually Sirius and Remus get together afterRegulusā death, Sirius would probably feel insecure and wonder if he wasjust the replacement for Regulus, despite Remusā numerous attempts at tellingSirius that despite their physical similarities, Sirius and Regulus are twovery different people that he loves for two very different reasons.
And there you go. Sorry for the long answerbut, yāknow, that stuff happens. I hope itās satisfying, and if anyone else hasa different opinion or something to add, feel free.