It seems weird to me that your roomates would go directly to the landlord without first coming to you to discuss any concerns or issues. Are you sure the landlord is being completely truthful, and not just saying things to make you get rid of the BP?

What does your lease say about pets? If the lease says no pets they could probably hold you to it, even if they let the scorpion slide by before. Did you discuss the possibility of getting a BP with your landlord and roommates before going out and buying one?

In the end, everyone in the house/apartment has an equal right to be happy and comfortable in the living space they pay for. If a majority of the people don't want the BP and your lease says no pets you may be out of luck.

Hope everything works out for you.