No puedo esperar a vivir contigo (informal)/con usted (formal) -or- No puedo esperar hasta que yo vive contigo (informal)/con usted (formal).
"Hasta luego" is neither formal nor informal, it straddles the middle between them and can be used in most situations. If you want a truly formal way of saying goodbye, "Adios" is probably the most formal. "Chao" correspondingly, should only be used between close friends or family members who are your age or younger.
it is an informal group
formal is the cinema and informal is a gay man
informal
It's both formal and informal. It depends on how you say it. If you say "Adiós, señora." it's formal. If you say "Adiós, amigo." it's informal.
formal and informal rhythm
what is formal and informal communication
formal
informal
what is formal and informal shareholders agreement
Formal is polite, informal is rude and obnoxious.