So Ryan fears both not being there for his friends who are back on earth And something about the future humans from Orphan 55?
yeah, I'd say so. like, he's realised that his friends are living life without him and the gaps between his visits back home are getting longer, so he's scared of his friends growing old and needing him when he physically isn't on earth. he's scared of earth being destroyed and missing huge events and eventually turning into a dreg.
it mirrors what actually happened to the Doctor quite nicely. she went away from her home for ages, only to return to see that it's burning and everyone is dead. I wonder where they'll go with that.
and obviously, that nightmare has made Ryan realise that he doesn't want to miss his friends' lives, his friends are all that he has left on earth, he doesn't want to grow older without them or vice versa and i can definitely see Ryan choosing to no longer travel with the Doctor by the end of the series, he isn't enjoying it as much anymore
