Seperation anxiety has been a very tough nut for the behaviourist world to crack. The main problem is the terminology. By calling it "seperation anxiety", which is a valid and correct term, we have assumed that everyone is reading from the same song sheet. Sadly we are not.
To the behaviourist (and I mean a real one) the term is used as if seeing the situation from the animal's eyes. In a dog's eyes the only anxiety created by seperation from the owner is if the dog does not feel safe. The only way that this can happen is if the dog does not trust it's owner to lead the pack (family) in a safe and consistent manner. The dog is given privelages that seem like kindnesses to the owner but seem like signals of dominance to the dog. For instance - the owner comes home from work, the dog rushes up, tail wagging, panting, nudging, perhaps even jumping up. The owner speaks to the dog, looks at it, maybe even drops everything to make sure the dog knows how happy the owner is to be greeted this way at the end of a long day. The dog's response to the owner coming home is highly ritualised and true joy is shown...BUT...it is ritualised for a reason. Any pack leader that has been away from the pack has been away for a reason - it may have been injured during a hunt or fight, it may have been looking for new pack members or getting rid of useless ones, it may have been marking the boundaries of the territory and looking for loopholes in neighbouring ones.....whatever - it is the boss that runs the pack. The rest of the pack all rush up and greet the leader on his return in order to gain information, reaffirm bonds and status within the pack and assess the security of the pack and the strength of the leader.
A confident leader will stand proud, ignore the greetings of the pack and even turn his face and eyes away from those trying to show how happy they are that he is back (the point is, the rest of the pack HAVE to go through this greeting to establish and reinforce the strenghth of the leader - physical, mental and emotional. The leader HAS to go through this every time to prove, without resorting to physical means, that he has the mental, physical and emotional strength to keep the rest of the pack fit, fed and safe.).
For most domestic dogs the life and mixed signals we give them about who is the pack leader is OK.
For 99.9% of the problems seen in domestic dogs it boils down to the issue of trust in the leader and who really is the leader.
The way you treat your dog when you return home has a massive effect on how that dog sees and understands your relationship.
Sleeping places also have a significant message for your dog - the best of everything goes to the leader...it has to. If you have a good leader then the rest of the pack is OK, so it pays to keep a good leader alive with the best food, the best sleeping place, the best breeding opportunities, the best support etc.
Allowing your dog to sleep with the people you are expecting the dog to see as it's leaders is a very confusing thing for the dog. You are telling it that it has the power because it has the best sleeping place and at the same time you are challenging that authority by allowing pack members that the dog has been encouraged to see as lower in the ranking system to have rights in the sleeping place. Your dog has no choice. It has been elected as the leader, it is being challenged, it is not able to distinguish between dog rules and human rules. It does not want the role of leader and so is forced into physical defence because it does have the signals from you or your boyfriend that you are better leader than it is.