From your point of view, it sounds pretty cut and dry since you would still be paying the rent yourself so there wouldn't be any problem if the bf skipped out.

However, the LL has additional issues to deal with. A second occupant uses more water and gas. They generate extra garbage and increase the wear and tear on a place. A LL also has a vested interest in knowing what kind of person this is. Will he destroy the place? A LL will want to do a credit and criminal history check. You may know your bf's history, but your LL does not, and there are enough boo-boos out there that he would not be exercising his fiduciary responsibility if he did not investigate any potential occupant.

Ultimately, the LL has the final say as to who lives in his property. If you are a model tenant and your bf is an above-the-board type of bloke, then the LL may be more likely to approve the additional occupant. But, barring legally prohibited reasons, a LL is free to approve or deny an occupant for any reason. It could very well be that the LL simply wants only one person living in your flat. That ultimately is his choice.

Hope it all works out.

Lighthope

Pearls of Wisdom - "Great mountains will one day be breaking, the trees fall to be decayed. Yet my love still won't be shaking, never will fade." - Forever Love (The Tigers' Second Quest)