What is done is done. Repentance is the most important aspect. Men and women have different psychologies. Fornication for men is different for women. For women it is usually because there is an absence of genuine male presence in her life. For a man, it can be jealousy over the "conquests" of other men, abuse of women, bestial lust and selfishness.
There are also virgins by desire - women who have lost their physical virginity but desire it back by spiritual means.
Now I am talking about Catholic men and women. For purely secular women, there are more reasons. But then again, ultimately, Catholics should really marry Catholics. Intermarriage of faith - while it can be part of God's plan - these marriages are more difficult than a purely Catholic marriage.
If a Catholic was going to marry a secular person (for whatever reason) then caveat emptor. Those who have drunk deep from that particular cup will find it difficult to go steady.
Marriage in the Bible is associated with faithfulness or idolatry. When Israel misbehaved it cheated on God and played the harlot with pagan gods. When it was faithful, then God blessed Israel. Fertility cults under Asherah Poles in pagan High Places and dancing around the Gold Calf "When Moses saw that the people were running wild (for Aaron had let them run wild, to the derision of their enemies), - Exodus 32:25) might have been a lot of "fun" at the time, but it ended in "disaster". People get a taste for than kind of cankerous way of life that is difficult to let go.