From infancy, my son would cry when I left to go to work. Through the early years, I was the calmer but more consistent parent. When his mother and I divorced, he lived with me - even had her parents willing to vouch that he was better off with me than with her. To this day (he is in his 40's now), we still have a strong relationship though very strong and opposite personalities. He does seek me out to rationalize his more impulsive moments or purchases! It wasn't easy as he grew older, but I had to remain consistent while also supportive and respectful. His mother, on the other hand, to this day still doesn't respect him or his decisions. Her loss. Thus, when I said that it is work - but very much worth it when one wants to be a parent - I know whereof I speak. Not easy, but definitely worth it.
As for the fact they are brothers by birth - psychologically, Matt will always be a father figure as well as an older brother.