Comments of chapter undefined of Multiverse And A Vampire

good author, please answer me the following: Why does he keep talking to his brother, if his girlfriend was unfaithful to him? I didn't understand why that obsession with the MC's brother, it feels somewhat forced but understandable with that he is a dragon. His girlfriend, if she was his girlfriend or just his childhood friend? If yes, she was his girlfriend, why was he unfaithful to her? If in fact they were unfaithful to him, why does he keep talking to his brother? And how come his brother doesn't know that his girlfriend was unfaithful to him with his brother? if from the first chapters the mc mentions it and the brother says that she hit on him and everything. (You had said that by chapter 7 we would know the answer)