Should I now file for divorce?

I have been married for 30 years. I discovered my husband's infdelity about 5months ago. He had pursued and even proposed to an ex-girl friend in high school, lying about his real status in life. They maintained a long distance cyber relationship. The girl now knows he is still married but continued encouraging him. My husband just left to see the girl and has a ring to give to her. Should I leave my husband now...file for a divorce?