@Tae Sis there were monsters after them,she was running for her life,it was no time for a group meeting. She realised that it might be too late for him because brother was stuck in a building full of monsters and moved on. What was she supposed to do? Tell others to go back to save him and get others who might have escaped killed too? Use some common sense,everyone is responsible for their own lives and it's not like anyone asked or forced the mc to save the girl. He ran out on his own knowing he is risking his life and if you do such stuff without consulting with anyone or telling anyone your plan no one is expected to pay you back. It's just like forcing your feelings on others,doing something for them knowing they never accepted your feeling expecting return.If he told them his plan I would get it too but he didn't,they were not supposed to wait for him.