He has left Islam three times
Question

                My question is I have left Islam and returned three diffrent times,I feel that the reason for this is the beliefs that I have had in the past are imbedded in me what can I do to establish true Iman wa taqwa and feel comfortably in this deen
Praise be to Allah.Allaah says (interpretation of the meaning): 
          
“Truly, the religion with Allaah is Islam” [Aal ‘Imraan 
          3:19] 
 “And 
          whoever seeks a religion other than Islam, it will never be accepted 
          of him, and in the Hereafter he will be one of the losers” [Aal ‘Imraan 
          3:85] 
 The essence of Islam is submission to Allaah alone, 
          by worshipping Him alone with no partner or associate, and by obeying 
          Him and His Messenger  (peace and 
          blessings of Allaah be upon him). The basic principle of Islam is bearing 
          witness that there is no god except Allaah and that Muhammad is the 
          Messenger of Allaah. Every Muslim must practise the religion of Islam, 
          devoting his worship sincerely to Allaah and following the Prophet  
          (peace and blessings of Allaah be upon him). Whoever adheres to that 
          until he dies will be one of the people of Paradise, but whoever does 
          not enter Islam before he dies will be among the people of Hell. Whoever 
          enters Islam then goes back (to kufr) is an apostate and a kaafir, and 
          if he dies in that state of kufr (disbelief) he will be one of the people 
          of Hell. But if he repents and comes back to Islam, and remains a Muslim 
          until he dies, his apostasy will not affect him, and he will be one 
          of the people of Paradise, even if he fell into apostasy more than once. 
          But there is the fear that this repeated leaving Islam will cause him 
          not to be guided to repentance. Allaah says (interpretation of the meaning):
 “Verily, those 
          who believe, then disbelieve, then believe (again), and (again) disbelieve, 
          and go on increasing in disbelief; Allaah will not forgive them, nor 
          guide them on the (right) way” [al-Nisaa’ 4:137]  
So hasten to repent sincerely and adhere to Islam, fulfilling 
          the obligations that Allaah has enjoined on His slaves, the greatest 
          of which are the five daily prayers. Avoid sin, and ask your Lord to 
          make you steadfast in adhering to His  religion. If you lose enthusiasm 
          then seek the help of Allaah and seek refuge with Allaah from the Shaytaan. 
          If you find that you are experiencing insinuating whispers which are 
          causing you to doubt Islam or some of its principles, then turn away 
          from them (those whispers), and seek refuge with Allaah from the Shaytaan, 
          and say “I believe in Allaah and His Messenger.” You should recite Qur’aan, 
          and read books which will make you love Islam and encourage you to obey 
          Allaah, such as Riyaadh al-Saaliheen 
          by Imaam al-Nawawi, and the Tafseer (Qur’aanic commentary) of al-‘Allaamah 
          ‘Abd al-Rahmaan al-Sa’di, Tayseer 
          Kalaam al-Rahmaan fi Tasfeer Kalaam al-Mannaan. Beware of 
          books which make you doubt Islam and make sin attractive to you. Beware 
          of bad company, for they are the devils among men. You should make friends 
          with those who will help you to remain steadfast. Beware of arguing 
          about matters of religion, for this causes anxiety and confusion. Strive 
          to worship Allaah, for He guides those who strive for His sake to the 
          straight path. Allaah says (interpretation of the meaning): 
 “As for those who strive hard in Us (Our Cause), 
          We will surely guide them to Our paths (i.e. Allaah’s religion — Islamic 
          Monotheism). And verily, Allaah is with the Muhsinoon 
          (good-doers)” [al-‘Ankaboot 29:69]