What does bernard mean when he says it might be possible to be adult all the time? why doesn't lenina understand

The thing is that Bernard spends the night with lenina. While they are walking all alone, because Bernadr does not like corwded places, he says to Lenina that not being a part of the social body is something that is worth to try to reach and that the system and the conditioning enslave the inhabitants of the city. Truth is that lenina does not understand a single thing and she gets offended.