[Orophin]

I think that Boromir knows that Gondor's strength is slowly leaving them. I also think that he knows that the only ally that they have had a kept from the begining is Rohan. Through everything thay have been there for each other and they cannot expect that from anyone else so I think that he has an interesting point. Although there are lots of people in middle earth the only one's that have always been there are the Rohirrim so he trusts them.