I was touched by sihr (impossible to marry). I've been treated by a fiqh. At the end of his treatment,he asked me to give him my ring. He did something with it, it will protect me against other spells. Is it haraam to wear this ring? Are my salaat and dou'as accepted? What should I do with my ring? Throw it, burn it,or pay no attention to it...? By wearing this ring, have I committed shirk?Please reply as soon as possible, Jazakallah.

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.

We ask Allah the Almighty to restore all Muslims patients to health. You are to resort to Allah, The Great and Almighty; pray to Him to make you well. Then, you should read more and more the Qur'an and remember Allah with all forms of Zikr as well as to come near to your Lord by doing more good deeds and avoiding misdeeds. Also, we advise you to make Ruqiah (Quranic verses and prophetic supplications) on to yourself via Qur'an and Du'a or to go to some scholar to do that on your behalf.
As for the person you visited, apparently he is a magician since he asked you to give him your ring to do or say what is believed to make you love or hate somebody. So, it is not permitted to put this ring on your finger if there is some material trace from this person's work, and you have to remove what is on it or to burn and wash it with water, when a Ruqiah has been done over it, and then you can wear your ring. But, if there is no trace except some supplications by a polytheist and so on, then wash it with water as mentioned above, and finally wear it, although it is better to avoid using it at all.
As for prayers and fasts, Insha Allah, Allah will accept your good deeds as long as you were in ignoraners or you have now returned to Him sincerely.
Know that wearing such a ring may constitute a state that is between major and minor shirk, i.e. this depends on one's belief. In other words, if you believe that such a ring will bring good or remove harm, then this is major shirk. But, if you believe that only Allah, The One who causes harm and good and the ring is just to rid oneself of jinn or evil eye, then this constitutes minor shirk.
It is reported by Imam Ahmad and Abu Dawood that the Prophet (Sallallahu Alaihi wa Sallam) said: "Ruqiah (supplication and so on) and Tamaem (a form of an amulet) and Tiwala (a form of magic done by a wife to make her husband love her) are forms of shirk." The ruqiah in this Hadith includes words of Shirk and talisman and mysteries.
Allah knows best.