He is
    suffering a relapse after he repented
Question

                I was brought up in a good Muslim household
      in the West. Unfortunately in my teenage years I allowed myself to be led astray by
      Shaitaan and committed many mortal sins for a number of years, even going out of Islam. I
      have tried to repent and reform over the last couple of years. I perform all the five
      pillars, give sadaqa generously, get involved with dawah and try to be helpful to Muslims.
      I am good to my wife and parents. However my heart is very shaky indeed. Sometimes I am convinced of the
      truth but usually I am "sumum bukmun". I find that my heart is very arrogant,
      evil and hates the Truth. I have tried hard to repress these negative feelings but cannot
      fully overcome them. I want to become a Muslim again but am at the point of resigning
      myself to a life of Taaghoot. I have read countless books and been to many lectures but I
      have made no progress. I want to succeed in this life and be saved from the Fire. What can
      I do? Do I need to do the Shahada again?  Please help me.
Praise be to Allah.His Excellence Shaykh ‘Abd al-‘Azeez ibn Baaz
    (may Allaah have mercy on him) was asked the following question:
I am a young man who has wronged myself by committing many sins. I do
    not even pray in the mosque, I have never fasted all of Ramadaan in my life, and I do
    other bad things. Often I have promised myself that I will repent, but then I go back to
    my bad ways. I make friends with young people in our neighbourhood who are not very good,
    and most of my brothers’ friends who come to our house are also not righteous. Allaah
    knows that I have wronged myself by committing so many sins and doing bad things, but
    every time I resolve to repent, I go back to my old ways again. I hope that you can show
    me a way to get closer to my Lord and keep me from doing these bad things.
He (may Allaah have mercy on him) replied:
Allaah says (interpretation of the meaning):
“Say: “O ‘Ibaadi (My slaves) who have transgressed
    against themselves (by committing evil deeds and sins)! Despair not of the Mercy of
    Allaah, verily, Allaah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful”
    [al-Zumar 39:54] 
The scholars agreed that this aayah was revealed concerning those who
    repent; whoever repents sincerely from his sins, Allaah will forgive him all his sins, as
    this aayah says, and as Allaah says elsewhere (interpretation of the meaning):
“O you who believe! Turn to Allaah with sincere repentance! It
    may be that your Lord will expiate from you your sins, and admit you into Gardens under
    which rivers flow (Paradise)” [al-Tahreem 66:8]
In this aayah, Allaah made the forgiveness of sins and admittance to
    Paradise conditional upon sincere repentance, which includes giving up and avoiding sins,
    regretting the sins of the past, and sincerely resolving not to go back to them, out of
    reverence for Allaah, hoping for His reward and fearing His punishment.
One of the conditions of sincere repentance is that one should restore
    what is rightfully due to people whom you have wronged or asking for their forgiveness if
    the sin involved wronging them with regard to blood, wealth or honour. If it is not
    possible to ask your brother for forgiveness concerning his honour, then you must pray for
    him a lot, and speak of him in the best way you can in the places where you gossiped about
    him, for good deeds expiate for bad deeds. Allaah says (interpretation of the meaning):
“… And all of you beg Allaah to forgive you all, O
    believers, that you may be successful.” [al-Noor 24:31]. In this aayah, Allaah
    made the connection between success and tawbah, which indicates that the one who repents
    will be successful and blessed. If the one who repents follows his repentance with faith
    and righteous deeds, Allaah will wipe out his sayi’aat (evil deeds) and
    replace them with hasanaat (good deeds). Allaah says in Soorat al-Furqaan,
    after mentioning shirk, killing without just cause and zina (unlawful sexual
    intercourse) (interpretation of the meaning):
“The torment will be doubled to him on the Day of Resurrection,
    and he will abide therein in disgrace; Except those who repent and believe (in Islamic
    Monotheism), and do righteous deeds; for those, Allaah will change their sins into good
    deeds, and Allaah is Oft-Forgiving, Most Merciful” [al-Furqaan 25:69-70]
One of the means of repentance is praying to Allaah for guidance and
    strength, asking Him to bless you with repentance. Allaah is the One Who says
    (interpretation of the meaning):
“And your Lord said: “Invoke Me [i.e. believe in My
    Oneness (Islamic Monotheism) and ask Me for anything] I will respond to your
    (invocation)…” [Ghaafir 40:60]
And He says (interpretation of the meaning):
“And when My slaves ask you (O Muhammad) concerning Me, then
    (answer them), I am indeed near (to them by My Knowledge). I respond to the invocations of
    the supplicant when he calls on Me (without any mediator or intercessor).”
    [al-Baqarah 2:186]
Another of the means of repentance which will help you adhere to it is
    keeping company with good people and following their example of righteous conduct, and
    keeping away from bad company. It was reported in a saheeh hadeeth that the Messenger of
    Allaah 
 (peace and blessings of Allaah be upon him) said:
“A man will be on the path of his close friends, so pay attention
    to who you make friends with.”
And he 
 (peace and blessings of Allaah be upon him) said:
“The likeness of a righteous companion is that of the seller of
    musk: either he will give you a gift, or you will buy something from him, or you will
    smell a pleasant fragrance from him. And the likeness of an evil companion is that of the
    man who works the bellows: either he will burn your garment, or you will smell an
    unpleasant odour from him.” 
(Majmoo’ Fataawaa Samaahat al-Shaykh ‘Abd al-‘Azeez
    ibn Baaz; Fataawaa al-‘Aqeedah, part 2, p. 640)
With regard to renewing your Islam: if you have done something that
    takes you out of Islam altogether, then you have to pronounce the Shahaadatayn and
    re-enter Islam because you had left it. If what you have done is a major sin which does
    not, however, take you out of Islam, then it is sufficient for you to repent according to
    the conditions referred to above. Do not despair of the Mercy of Allaah; follow the path
    of salvation. May Allaah give us and you the strength to do all that is good. May Allaah
    bless our Prophet Muhammad.
We ask Allaah to bless us and you with sincere repentance and to forgive
    us and you. May He show you the way out from your problem and bring us and you together in
    Gardens of Delight (Paradise) facing one another on thrones [cf. Al-Hijr 15:47]. Ameen.