What's happened now, Jann?
I don't think you can be friends with a pukka BK. At best, they will either be 'using you' or 'serving you', neither is real friendship. A BK cannot have friends even within the cult as it involved sharing, bonding, attachment and so on.
In your case, it seems that the relationship with your friend has always been ambiguous because he was "having his cake and eating it", i.e. enjoying the benefits of your friendship/your heart but giving his heart to the BKs rather than you.
If so, no wonder you feel empty; you have given but not received back.
There are other fish in sea, other battles to fight, other lives to live. The BKs will just keep on being the BKs and doing what the BKs do, which we have studied well.