I dont think they made up, relationships are obviously not going to stop from argument like these they'll continue to be girlfriends but I'm sure in the back of their head it exists, I'm assuming this is just leading to a huge fight in future chapters with the brother now being unsure if their love is normal
Also yes the brother was introduced before he's a twin, they were introduced early in the chapters by they don't make an appearance much

Am I trippin or did I miss the part where they made up? Also when was the brother introduced before? Did I jump to another dimension without knowing it or was I high when I read those chapters?