I agree: "This is called a relationship boundary cross block."
This is what people in exclusive relationships do when they are not wanting to give a member of the opposite sex "the wrong idea." If you're sincere in your assertion that you don't want to give him the wrong idea, then you will incorporated "relationship boundary cross blocks" whenever this new "friend" attempts to cross your relationship boundary(s).
Hopefully your bf would be doing the same thing when he interacts with members of the oppposite sex that he grabs a bite to eat with as well. It's how people who have promised exclusivity to one another avoid getting too emotionally involved with other people that we may find attractive. Blocks reinforce to him/her and more importantly YOU that you are in a relationship.