Starting Over (1979)

Burt Reynolds is an attractive middle-aged man who suffers a crisis of confidence when ditched by his ambitious singer wife (Candice Bergen), until he begins to forge a new new relationship with an equally insecure teacher (Jill Clayburgh). But when the wife attempts a reconciliation--seduction followed by a truly excruciating song she has composed for him--he realizes where his loyalty lies.—alfiehitchie