Cheating Question BF and GF Debate

1. If a girl cheats on her boy friend with her music teacher but wants to stay in touch with him because she wants to still use him as a music teacher, should the boy friend allow it?
2. The boyfriend who has not cheated works with an ex girl friend who is engaged and he has no interest in her at all. Should the girl friend be worried?

3. The girl friend believes that if the boy friend can see the girl she should be able to see the music teacher. Whats your opinion?