Caleb was the boyfriend of Ian.
Ian met Caleb at the local fire station, in Going Once, Going Twice, while seeking to thank the fireman who rescued him in the previous episode.
Attracted to him, Ian flirts with him throughout Refugees, however, when he makes a move on him, Caleb explains his want for a relationship instead of the sexual encounter Ian proposed. Ian, taken aback by the normality of this, explains his past relationships' abnormality, however agrees to go on a date with Caleb.
In the seventh season, Caleb cheated on Ian, proving his "bisexuality". But he does not think it is cheating, so his relationship with Ian is over.