pragmiser

A person who insists on destroying any hopes and/or dreams you have; by saying they're too unrealistic or unreachable .
It can also just refer to a person who's trying to make people think more pragmatic in other, more positive situations, but is usually used as an insult.
A bit like how "Bitch" has a completely innocent meaning in the right context but is widely used as an insult.

Paul is such a pragmiser ; always bringing me down. Saying my dream of becoming an Astronaut , will never come to fruition . Worst part about it is... I think he's right.