Ok, I've read that you can miss Danse's perk by going too far before you get it, so I'm trying to grab it now, but I can't seem to get it going. So far from looking around on the internet all I can find is that I need to 'do quests for the brotherhood'. I don't have any further quests that I can do for them though....can anyone point me in the right direction? I'm not worried about spoilers....kinda know more or less what happens.

Ok....after some further searching it looks like I may have to do Blind Betrayal before I get the perk? Can anyone confirm this?

Yes, you have to complete Blind Betrayal before you can max out your relationship level with Danse and get his perk.