'Black lives matter, but I'm white'
The best thing we can do to join the alliance of our Black friends is not to ignore race, or be overly sorry about racism, or overload our friends with questions about things you'd 'never even considered before'. I can guarantee you that they have had to consider it a long time ago. Educate yourself, consider it, and then talk to your Black friends. Try not to express shock, or hurt, so explicitly. Instead, show them through action and open conversation, that you are with them for the long haul.