Praise be to Allaah.
If the women was as you describe before you got engaged, then it is not permissible to marry her unless she repents sincerely for the sake of Allaah, not for the purpose of getting engaged to you. If you see that she has repented and regrets what she did, and that she is serious about keeping away from non-mahram men and avoiding being alone with them, then it is permissible for you to marry her.
My advice to you is to look for a righteous and chaste women, for a righteous wife will bring you happiness in this world and will be one of the means of your salvation in the Hereafter, because she will one day be the mother of your children, and she will guard your honour and your wealth, and in that way there will be the love, compassion and tranquility that form the basis of marital happiness. Allaah says (interpretation of the meaning):
“And among His Signs is this, that He created for you wives from among yourselves, that you may find repose in them, and He has put between you affection and mercy”
The Prophet (peace and blessings of Allaah be upon him) said: “Women are married for four reasons: wealth, beauty, lineage and religious commitment. Choose the one who is religiously-committed, may your hands be rubbed with dust (i.e., may you prosper).” Narrated by al-Bukhaari, 3/242; Muslim, 2/1086.
According to another hadeeth: “This world is temporary pleasures and the best of the temporary pleasures of this world is a righteous wife.” Narrated by Muslim, 2668.
With regard to what you mention about what happened with that other girl, praise be to Allaah for having enabled you to repent. This is the bounty of Allaah towards you. You have to strive to control yourself and avoid the things which lead to such serious consequences.
We wish to point out that repentance must be for the sake of Allaah, not for the sake of your fiancée and so that she will be sincere towards you. So we advise you to renew your repentance and to pray for forgiveness and to make a promise to Allaah not to do such a thing again.
I also offer the following advice, and hope that Allaah will benefit you thereby:
1 – Lower your gaze and do not look at that which Allaah has forbidden.
2 – Keep yourself busy with reading Qur’aan and hadeeth, stories of the righteous, the scholars and ascetics.
3 – Beware of being alone with women who are not mahrams.
4 – Keep company with righteous people who will help you with religious and worldly matters.
5 – Beware of listening to music and songs, for they are a means that lead to zina.
6 – Strive to offer prayers regularly with the Muslims, and strive to observe all the essential parts of prayer with proper focus and humility, and having wudoo’, for it keeps one away from evil actions, and those who observe regular prayer are the ones who will succeed. Allaah says (interpretation of the meaning):
“Successful indeed are the believers.
Those who offer their Salaah (prayers) with all solemnity and full submissiveness”
May Allaah help us and you to do all that is good, and may He make things easy for you.