Another Woman.

Anya and Valera Khokhlov married in their youth out of great love, lived together for seventeen happy years, moved around military garrisons, and raised two children. The idyll collapses when Valera decides to leave the army to go into business and brings his family to a big city. At her husband's birthday party, Anya is horrified to discover that Valera has a mistress—the vibrant and sexy Nika, the director of an advertising agency.