In Alien Hunter Dick admits that he's an alien to Charlotte, and then tries to pull a Heroic Sacrifice by telling her he's the only one and the others are innocent bystanders.
In The Big Giant Head Returns, Dick finally gets fed up with how the BGH has the nerve to just interrupt their lives and try to take Vicki away from Harry, knowing he'll probably be consigned to some horrible fate on the other Mars.
This is followed by Harry, touched by Dick willing to sacrifice himself for his sake, telling Vicki that she should be with "Stone" (the BGH's fake name), because, despite everything, he seems to genuinely love her, and Harry doesn't want Dick getting hurt.
Dick doesn't mind when the BGH's niece, who's been posing as his wife, insults his looks and his personality. But when she insults his family, that's when he gets mad.
However, when Janet announces she's going to explore the world, Dick takes a moment to warn her out of concern that the world is a big place.
The episode has seen Dick separated from Sally, Harry and Tommy for months due to the previous season's cliffhanger. He kept hoping they'd come back and went back to the same spot they left from every night afterward.