I'd guess a 50cm frame would be too small for a guy who is 5'11". I'm 6' and I ride a 58.
There isn't enough info on the first one.
Is
this a possibility? It isn't C&V, but does he prefer C&V bikes? It is small, but from what I remember of your bf, he rode a little bike for his size.
Posting his old bike again for ease of seeing what size he rode.