It looks like he’s mourning what could have been. Like maybe if Mickey had come out sooner, somehow Ian wouldn’t be bipolar. If Mickey hadn’t married Svetlana, none of this would have happened. If he had told Ian not to go, Ian would be okay. If he had listened to Fiona, maybe Ian wouldn’t be in the psychiatric ward. They would’ve had time, and Ian would be okay.
This wasn’t supposed to be Ian’s life, and it looks like Mickey blames himself for that.