Do you think James and Sirius got into a fight/argument after Sirius tricked Snape into going into the Shrieking Shack? And how long do you think it lasted? I feel like Marauder era fans ignore this scene, but I think it is actually really important. I think there was a disagreement and it was heated. I also think they were cool the next day. They aired their grievances and moved on.
Owl:
That’s a good question. I’ve discussed my personal headcanons about how it happened, but basically I think Sirius was with James (or Peter or Lupin) when he realized that Snape was eavesdropping in some way or another. Sirius rashly decided to teach him a lesson by oh-so-casually mentioning the Whomping Willow. To Sirius, this was justified punishment to someone that was a dark wizard and trying to get them expelled. But he absolutely didn’t think through the consequences to Lupin.
I think James would be (justifiably) extremely angry at Sirius. More because Sirius endangered Lupin than because he endangered Snape. I also think that because Remus tends to be a little more passive, James would subconsciously take on Remus’s anger as well.
I’ve talked about this before, but Sirius is someone who’s relatively flexible morally, and has basically learned his entire system of morality from his friends. So James’ anger and disappointment would be a huge blow. Sirius has also been raked over the coals by Dumbledore, another person he greatly respects. At the end of the day, regardless of Sirius’s feelings toward Snape and the degree of remorse Sirius feels about the potential consequences to Snape, Sirius knows he screwed over one of his best friends. And given that Sirius would literally die for his friends, that’s a huge deal. So Sirius is already in a bad place, and James would recognize that.
I think it wouldn’t take more than a day or two for James/Sirius to be spending time together again, but I think the relationship would be forever changed and James would never quite look at Sirius as he did before.
Though TBH Hilary and I have had like 2 bottles of wine between us, so maybe don’t trust either of us.