No, you can't do that. A text message only goes to the phone it was sent to. There is no other place they can be seen.
You can't. It doesn't work that way. The only way you could read his incoming text messages is if you were holding his phone.
AFAIK you can't receive messages on your phone that were sent to another phone, but you can forward messages from one phone to another.
It also depends on the situation that qualified you as well as your past employment, if any.
Please restate your question with more details to explain what you mean.