The Prisoner briefly reuniting with his fiancé in "Do Not Forsake Me Oh my Darling." Despite being in a different body (long story), he eventually manages to convince her that it's really him and the two share a passionate kiss. Yeah, they used a different actor for this bit, but the effect is so powerful and the performances so believable, that it doesn't matter in the slightest.
"The Girl Who Was Death" ends with The Reveal that the whole episode was just a story No. 6 was reading to the children he was babysitting.
Number Six's friendship with Number 24 (AKA Alison) in "The Schizoid Man." The two appear to genuinely like each other, to the point that both are visibly upset when Alison is forced to betray Number Six as part of Number Two's plan. She even apologizes to him for it later.
Number Six and Number Two Leo McKern putting aside their differences and past concerns to escape together in the final episode.
