My friend and her boyfriend live in their own world, is this normal?

My friend and her boyfriend have been dating for over two years. Almost every night he makes dinner for her, and they barely go out. Recently her foot has been messed up, so she can’t walk or do much, but she didn’t really do much before that.

She claims to be happy, but I feel like at 26 it just isn’t normal to always be at home. She says that he gets jealous of our friendship even, and that she doesn’t want to make new friends because she doesn’t trust people. He has no friends that I know of. Is this a healthy relationship? If it is unhealthy, how do I tell her what I think?