Firstly, you and your partner need to sincerely repent to Allah and do a lot of righteous deeds to make your receptance acceptable. As you said that it was a haraam relationship then it could mean that you committed zina which is one of the major sins of Islam and even the hadd punishment for it has been given in the Qur'an and Hadeeth.
Repent!!! Repent!!! Repent!!!
Righteous Deeds!!! Righteous Deeds!!! Righteous Deeds!!!
Only these things can help you.
You cannot even marry your partner until you repent because marriage of a zani and zaniyyah isn't called valid under the sharia'h. Read the Q&A in the following link: