Dispassionate describes someone who is not getting carried away by—or maybe not even having—feelings. It's something you'd want to see in a surgeon, who keeps cool under pressure, but not in a romantic partner.
Dispassionate is the opposite of passionate, and while passions are said to run "hot," dispassionate people are often described as "cold." A city marshal whose job is it to evict people behind on their rents must conduct their job with dispassionate fairness, but still, no one wants to be their friend.
