Here's a seldom taught trick for this kind of thing. Do a Google image search for the term and scrutinize the results. That should tell you how people actually use the term better than a standard search.

In the case of 相方 (aikata), you mostly see two men or a young man and woman. This is congruent with the English use, which usually refers to men in a business relationship but also can be used by young people in a relationship.