In Shadows of Undrentide, ask Tymofarrar Deekin's freedom and he will give you the stuffed doll for Deekin. Upon examining, there is a note from Tym to Deekin with the doll: "Search for your dreams, lad, and good luck. - T.".
At the start of the final battle in Hordes of the Underdark, Mephistopheles attempts to turn your henchmen to his side. There are several options you can use: a high Persuade score will turn them back, or you can use their True Names if you know them. If one is your love interest, you can use The Power of Love. But for Deekin, you don't need any of these, all you have to do is tell him you'll miss him. Aaaw.