Your GF wields a Yashica Mat? - Keep her.
What lens or lenses are you going with?
I will probably use the 150/4 quite a bit, as my father owns two of them, so it won't take away from his kit if I take one on extended loan from him
He has two 80/2.8s as well, I believe, so I'll take one of those too.
I'd like to get something wider at some point as well, like the 50, but having shot excessively with the 75/3.5 on my Rollei, and the 80/3.5 on my girlfriend's Yashica, I'm not too concerned about immediately acquiring additional lenses. Mainly, I'll welcome the extra speed and more precise viewing of the Hasselblad.
And yes, I'm very happy to have a girlfriend who is interested in film photography, she also has a Nikomat with a stable of lenses at home. She's essentially my other half.