Husband tormented about love 16 years ago

I am 45 years old, running a small company; husband over 2 years old, is the general manager of a large corporation. Recently, I find out and know her husband similarly, tormented about the past love affair.

My wife and I have been married for 12 years, having 2 daughters, the first one is 12 years old because I was pregnant before I got married. I heard briefly about his past love, then know that love was formed about 16 years ago. When I was young, my husband was an engineer in a construction project in a central province. She was 10 years younger than my husband, very beautiful, good-natured and gentle. For some reason, she left him, and after a few years, he got to know me and he was in love with me.

Now he frantically searches for her on every channel, social network. I know they met again. My husband still treats me well, except that he is always pensive, silent, fulfilling his role and obligations. I love my husband very much and feel confused about my family's happiness. Please give your advice.