Kevin is a mentioned-only character in Fallout 3.
Kevin was a wastelander who was slowly dying of severe radiation sickness. His brother tended to him, but there was not much he could do. Eventually, his brother sent the marry me! holotape to the woman he loved, but she also died in the Wastes. The fate of Kevin and his brother are unknown, but it can be assumed that Kevin succumbed to radiation poisoning and died.
Kevin is only mentioned in Fallout 3.