Most Helpful Guy
If you go after her then you need to forget about ever being friends with this guy again. If you are okay with destroying your relationship with him, for a girl then go ahead. Chances are you aren't that close anyway. As long as he isn't actually your real brother, then you would still be connected to a guy that you hurt. Doing that could destroy your family. Since he is just an acquaintance it isn't as big of a deal. Go ahead and date her if you want.