They have a responsibility to let you know IF them running for prosecutor presents a conflict of interest: that is, it it will diminish the lawyer's ability to properly represent your boyfriend, because, for example, he has to show he's "tough on crime" and so can't defend your boyfriend properly or negotiate hard for a good plea. If you fear this is the case, ask them to transfer the matter to a different lawyer; if they won't, you may wish to contact the state bar assocation about possibly filing an ethics complaint.