Student in a boarding school sleeping in a place safe from sin

Q: I go to an all boys boarding school, and in the dormitory, when it's time to sleep, there are many boys that watch movies in the rooms, and they do all other sorts of Haraam in the room. 

If there is an alternative place for me to sleep, such as a close by Masjid, or the library, is it permissible for me to sleep in the dormitory?

Businessman preventing two people from transacting a sale on his property

Q: Could mufti advise on the following: 

Person A owns a Cash n Carry, person B and person C both are his customer's and purchase from him. At the premises of person A, person B and C meet and start transacting on person A's premises. Person A in turns tells Person B that person C is my customer and you cannot supply him. 

1. Is this type of clause permissable in shariah where person A stops person B from supplying person C as he feels it's his customer. 

2. If person B and C transacted on person A's property, is the sale valid.