Jegulus head cannon?
James liked Lily and they dated but had to breakup because things were complicated or were on and off at first and at a party James ended up messing around with Sirius's little brother and they kinda did just in general for a bit until Regulus(Abt sixteen I think) got the dark mark and they got in a huge argument and James didn't tell anyone about any of it and over time his love for Lily trailed back and they ended up together and stayed together. No one knows abt what happened between James and Regulus besides Remus, Barty, Evan, and Pandora(if you like the Slytherin Skittles/ the Pantheon then Dorcas too, no one cares if Barty seemed more Ravenclaw or if Dorcas is a Gryffindor)