If you're thinking of the classical sounding instrumental with the flute, played as Warren is going to sleep and then transitions into the wedding, that's "Longer" by Dan Fogelberg. I've never heard it like that, and it is a beautiful song.
Tracklisting 1. The Adventurer [1:38] 2. Telling Ndugu about the Family [3:38] 3. About Schmidt [1:29] 4. Schmidt Went to Denver [1:50] 5. Randall's Room [1:17] 6. Guilty Escaping the Rusks [1:03] 7. Helen Goes, Schmidt Stays [2:46] 8. Of Life After Helen [2:26] 9. The Fury of Schmidt [2:30] 10. Shopping with Schmidt [2:02] 11. Missing Helen [1:27] 12. Riverside Prayer [3:09] 13. Dinner with Randall's Relatives [1:01] 14. Schmidt Revisited His Alma Mater [1:26] 15. Schmidt At The Wedding [1:37] 16. Omaha Return [3:05] 17. Ndugu's Painting [1:05] 18. What I Really Wanted to Say [1:31] 19. The End Credits [2:23] 20. Constantine & Warren [1:30] 21. Africaan Beat - Bert Kaemphert [2:27] 22. Ndugu Letter [6:19] 23. Interview with Alexander & Rolfe [15:05]