Growing up, Sirius didn't really have much people to call his.
So naturally it was hard to accept that James was going to date Regulus whether he liked it or not.
It was even harder to come back after Azkaban and find that Remus had tried a few relationships in those twelve years. Anytime an old flame pops in, he'll cling onto Remus and kiss him
Honestly, does it in public too. Big ole abandonment issues and fear of losing Remus because in his mind, he's not worth love but he's got it and will make sure people know.
The cashier at the store who laughed at Remus' dry humor about whatever purchase they had? Threat
The bus driver who smiled at them both? Threat
A young Stan shunpike on the knight bus with the same accent Remus has that drives Sirius? Big fucking threat
