According to our Big Book, the sponsor should be known to you. " If there is any indication that he wants to stop, have a good talk with the person most interested in him, usually his wife. Get an idea of his behaviour, his problems, his background, the seriousness of his condition, and his religious leanings" You need this information to put yourself in his place, to see how you would like him to approach you if the tables were turned."
The book suggests maintaining contact with the sponsor even when he is drinking because there will be lucid moments from time to time where your boyfriend may be open to getting help, usually after a bender.
Sponsors are not supermen, neither do they have special divining powers. Good sponsors keep an eye on their sponsees through a variety of sources. Like the talk with the wife, background info can help the sponsor figure out how best to approach the subject.
Keeping the sponsor out of the loop is just another form of enabling or denial.
On the other hand, a sponsor would not be willing to disclose any informtaion given in confidence. 'Another principle we observe carefully is that we do not relate the intimate experiences of another unless we are sure he would approve."
I would say overall that you can work with a sponsor to help the subject by filling in background that will help, but that relationship is not to be used for gaining information for any other purpose. Your own peace of mind would be better served through something like Alanon.