Emissary (Star Trek Deep Space Nine) by J. M. Dillard

Commander Benjamin Sisko is just recovering from the death of his wife when he is assigned command over the former Cardassian, the new Federation space station, Deep Space Nine. This space station is strategically located not only because of its orbit about Bajor, but also because of its proximity tot he only known stable wormhole in the galaxy. After meeting the other Bajoran and Starfleet personnel assigned to the station, including a former Bajoran freedom fighter and a shapeshifter, Sisko finds himself in that very wormhole and in the midst of a metaphysical experience as the alien inhabitants of the wormhole question the concepts of time and love. Sisko, filled with humanistic hubris, begins to explain these experienced, and resolves his painful past.