That's an interesting question, yet seems somewhat difficult to study. Several studies show that couples in "hostile relationships" do heal slower than "health

That's an interesting question, yet seems somewhat difficult to study. Several studies show that couples in "hostile relationships" do heal slower than "healthy relationships" (fighting affects the immune system). But I haven't been able to find anything with data regarding immune responses in "hostile relationships" vs being single. Those in hostile relationships have already increased their lifespan, although the hostility was likely not present for the entire relationship.