Assalamu Alaikom.Dear brothers in Islam, I come to you with tears in my eyes and pain in my heart... and love and need for mercy from Allah (Subhanahu wa ta'aala). About 3 weeks ago I married an Asian woman who is 26 years old. She converted to Islam by herself after she studied the religion for 6 months. She is a nice and gentle believer who prays regularly and is learning Qur'an and Sunnah with me. She had a very serious problem with a man who is 75 years old (before she became close to me). I have doubt (Shakk) that she had commited adultery with him BEFORE she became Muslim. I keep feeling jealous and want to find out but she said that nothing happened. Yesterday I found a paper from her to him that said she loved him... but that paper was old. So we had an argument and she was angry... so I left the house to calm down... but she thought I was going to leave her.... so she came down in the freezing weather to bring me home. After that she wanted to leave me and stop the marriage. I asked her to calm down and after about 1 hour of negotiation she calmed down and we prayed and slept. Now she is ok and I am still unhappy with what I did... I feel guilty that I am giving a bad impression to this very new Muslimah. I am stuck... and very sad... but hopeful that Allah (Azza wa Jal) will help me, Sometimes I feel that I should forgive and forget everything before we married... and sometimes I feel that I should investigate and find out to calm myself, I want her to be my wife forever, Insha Allah... I love her and would do anything for her...Please help me.

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Dear brother,
It is narrated in Sahih Muslim in the story of the Amr Ibn Al 'Aas's death that the Prophet told him when he became Muslim "Are you not aware of the fact that Islam wipes out all the previous (misdeeds)? Verily migration wipes out all the previous (misdeeds) and verily the pilgrimage wipes out all the (previous) misdeeds".
Since Islam forgives everything that was done before it and since you certify that your wife is a good Muslim who applies Islamic teachings in the right way (praying, reading the Qur'an….), you should not investigate her past, because all her past sins even polytheism, which is the greatest sin, have been forgiven, because of her Islam.
Know also that the Prophet told men not to enter - after a trip - their wife's dwellings at night "In order to watch their stumbles". [Muslim]. So, forget about her past and do not investigate it as long as there is no new matter that makes you doubt her behaviour.
As for your jealousy which was brought about by what you found out and which resulted in the argument you had with your wife, we hope that it will be forgiven, as jealousy is usually out of the control of the person and it is not punished as long as it does not affect the rights of other people like the wife…etc.
Allah knows best.