Of course there is an other. Dasein is in-a-world-with others. That means, the Dasein is constituted by the other. This includes living breathing other human beings and it includes history, culture, and society. Dasein is disconnected from others.
Ethics is another matter. There is no ethics in Being and Time — to no ethics concerning an other. Heidegger makes it clear that authentic Dasein makes its own choices without reference to written or established ethical or moral codes. Dasein makes choices for its own possibilities — but does this within history and within community.
In Heidegger, death is non-relational. This is often understood to mean that Heidegger ignores intersubjectivity. That is a mistake.
Heidegger is NOT the philosopher of intersubjectivity, but he does not ignore it. Dasein is always already in a world of the other.
Heidegger addresses empathy, too. He remarks that the topic had been framed in a misleading way. He doesn’t disagree with Husserl (or Stein — I need to look up the section to see how close his reference is to S), but thinks the discussion doesn’t include the structure of being in. Dasein is not a subject, but the ontico-ontological condition, as it were, for a subject, self and ego, an other. Dasein’s being, then, as a being-in-the-world of other Dasein’s is condition for the emergence of self and other. “We” are always already connected with one another is a felt, sensed, primordial, ontological way, as beings-in-the-world. (Read: mirror neurons).
Empathy is privative in that it describes a state of Dasein once removed from sense of this world and into an ontic world where self and other, subjects and subjects, are differentiated — as entities.
I am doing a presentation at an upcoming GT conference “Talking in the House of the Other: the Ethos of Dialogical Contacting.” One of the my basic points is that we are always in “a relational home,” a world into which we are thrown and in which we develop — an historical and specifically relational world of people. It is the ground upon which we walk, the walls that shelter us as individuals.