He is involved in Da’wah but feels that he is a hypocrite and weak in faith

I have a VERY important and urgent question. I would really like a DETAILED answer as your answer could change my life !!! Mail me if you want more information.
Please be patient with the length of my question as I believe the more I inform you the better you can answer the question.
I live in the West and I was born in a Muslim family. From my early teenage years I became active in Islam. Even from a young age I believed in Islam and I even wondered how people went to sleep without praying !!
I'm now much older and I have changed completely. My belief in Islam and even in Allah has disappeared. Basically I have become an outright hypocrite of the worst kind. I stay away from women but not pornography. I am prepared and trying to give that up and that maybe the cause of my fall but I've noticed that it's too late, as this is now a branch of the problem and not the root as the root of the problem is my belief in Allah and Islam.
Sometimes I believe I am crazy as I continuosly have erroneous thoughts about God, where I came from, Islam, right and wrong, etc.. I seem to be fighting between belief and disbelief, especially during prayer.
I have not abandoned prayer, etc, but it really does not benefit me any more. If you meet me you'll think I'm practicing from my appearance and speech, etc, I go to the mosque, I fast, but really I'm a true hypocrite whom no one knows. I cannot go on like this.
I actually actively give Dawah aswell to non-muslims but in my heart I really disbelieve, so why am I doing this ??? But when I directly discuss Allah it hurts me due to my confusion as I have lost my belief and find it hard to fake belief at times !!!

Praise be to Allaah.

You should know, my brother, that the most essential thing for any person is his commitment to Islam and his faith, and he will not be harmed by whatever he misses out on of worldly things if Allaah keeps his religion safe. Allaah is the King of kings and is the One Who moves the heart; He Alone is the One Who strengthens the heart and makes it steadfast. For this reason I advise you, my brother, to turn to Allaah, for He is a loving and merciful Lord Who is Compassionate towards His slaves. If you turn to Him sincerely and pray with true longing and ask Him to strengthen your faith and protect you from the evil of the whispers of your own soul and of the Shaytaan, then Allaah is Close and responds to the prayers of those who call on Him. Do not forget this important fact, for it is a source of relief and a way out from your problem, in sha Allaah. I would also like to remind you of the virtues of reading Qur’aan and reciting a lot of du’aa’s, morning and evening, for this will have a great effect in bringing peace and comfort to your heart.

Avoid the things that will make you feel far away from Allaah and bring you closer to the Shaytaan and his whispers. One of these things is what you mention in your question, namely looking at pornography and so on, because if a person persists in sin, it piles up in his heart until it is overwhelmed with darkness and is not affected by any exhortation or preaching. So hasten to repent from this sin and others, and fulfil the conditions of repentance properly. We also advise you to avoid sitting with bad company and in gatherings that could increase your confusion or provoke your desires; look for good people and keep company with them, because a man will be on the religion of his friend.

It seems from your question that you are suffering from a specific psychological problem, either financial or social or otherwise, and this is having an effect on this waswaas (insinuating thoughts from Shaytaan) that you are suffering. If this is indeed the case, we advise you to treat this problem quickly, because this may be a way of dealing with what you are suffering from. We will help you as much as we can, in sha Allaah.

What you are going through might be a kind of depression or anxiety, for one reason or another. You know that Allaah has not created a disease without also creating the cure. It is known that there are medicines that may be of help, by the grace of Allaah, in treating this kind of sickness. So ask about this kind of medication from a psychiatrist.

Islam Q&A
Sheikh Muhammed Salih Al-Munajjid