I have a very severe problem I loved someone we were very happy together. After a period a person from my family wanted to be engaged with me. I could not decide what to do, especially that my family agreed his proposal. So, after a period of stress and problems I went to some one (a magician) and I asked him if this engagement will succeed or not. He told me no, and I told him that I love some one else I don't want the one of my family. Then, he told me nothing but after a period I was surprised by my ex-lover interrogated me, saying that I bewitched him and he was ill, and don't sleep during three months. After that he went to a magician, he was told that the girl he was with her (me) bewitched him. When he told me I surprised because I did not involve in any such practice. I regret for what I did because no one can be aware of the future except Allah. I ask God for forgiveness day and night even if I did not know what the magician did to make him ill.Now I seek always with my ex-lover to forgive me because I do not want to loose him ...but he swears that even if he forgives me he will never come back to me (we were deciding to be married after a while because of his bad situation). I think he is a good Muslim but he considers what I did as an unforgivable sin. What do you advice both of us?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Indeed, an evil deed leads to other evils and a sin leads to many other sins. When you committed what is forbidden i.e. having illicit relation with this alien man, Satan pushed you to commit more repulsive sins that are going to jugglers and magicians and dealing with them which are strongly condemned in Shariah.
In fact, practicing magic and soothsaying, asking the help of magician and soothsayers and believing in them are totally forbidden In Islam.
The Prophet (Sallallahu Alaihi wa Sallam) said: "Whoever goes to a fortune-teller and asks him for something, his prayers will not be accepted for forty nights (days)." (Muslim)
Therefore, you should turn towards Allah in a sincere repentance for these illicit relations, for going to magicians and immediately cut off all the relations with the person (ex-lover).
Know that a sincere repentance consists of giving up the sin, feeling deep sorrow for what happened and taking a firm decision not to recommit it. We ask Allah to guide you and us to the right path.
Finally, know if your relative is religious and good-natured then accept his proposal and get married with him turning away from this person(ex-lover).
Allah knows best.