I haven't actually seen many reviews that comment on the sexuality aspect of Dust, though one referred to "lesbian chic." I have seen several that felt the characters were distant and unreal, however.
But yes, very very bothered. In Blood and Iron, I was bothered by other aspects of the plot as well, and in Carnival it could almost be excused because the lesbian couple were such background characters. Dust, though, shows a trend I really dislike and am wary of.
I keep going back to Bear's books because the worldbuilding is so awesome and full of potential, and then I bounce off the characterization and remember why I had a problem with her writing in the first place.
I think this may be my problem, too, and I'll just have to accept it. The only one of her novels I liked unreservedly was New Amsterdam. With all the others, there's always a wall that keeps me from enjoyment. Normally not quite as severe a one as it was with Dust.
The Female Man by Joanna Russ has lesbian characters who don't die. But yeah, outside feminist science fiction the number is very small.