Comes/comites is translated with comrades, and contubernalis with tent-mate, in another Duolingo's sentence.
I think they can be both synonyms, but Comes is more a friend, a comrade, and Contubernalis someone who share a room or a tent (so, with a meaning of "friend" later in history)
Note that the word comrade in English has the same meaning etymologically, it comes from French camarade, and camarade comes from Spanish camarada = people who are in the same room (army, board school, etc...)
I think we could also use companion, as compagnon is etymologically someone who what you share your bread (= a close friend), from French com/co-pain/pagnon/pagne/pine.
Co-pain = same/share-bread.
Comes gave French Comité, anglicized later in Comity.
Etymologyonline says than Comité is from Latin comitas "courtesy, friendliness, kindness, affability," from comis "courteous, friendly, kind," but I find it more logical it comes from Comites, as comites really have the meaning "to be associated with".
Contabernalis is Con + taberna.
Sharing a taberna! What's weird.
Yes, it is from a later area. In Classical Latin comes was a companion or a comrade, etymologically, "a person that goes with another person". In Classical Latin dux meant "a leader", "a general". In Medieval Latin comes came to mean "a count"; and dux, "a duke". From these late meanings related with the nobility, the musical terms to which you have referred must come.