As-salamu `alaykum.

Dearest brother, there is nothing in the world that brings sorrow to a fellow Muslim more than to hear of one despair of the mercy and forgiveness of Allah. My heart truly goes out to you for what you are feeling. I will start by providing you with a litany of evidence to help you see that you can NEVER despair of Allah's mercy.

I will start with the famous Hadith Qudsi, that puts everything in its place. Allah said very simply "My Mercy Prevails over My Wrath "

{ "Say: O My slaves who have transgressed against themselves! Despair not of the Mercy of Allah, verily Allah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful."} (Zumar 39:53)

In another Hadith Qudsi: On the authority of Anas, may Allah be pleased with him, who said: I heard the Messenger of Allah, peace be upon him, say: Allah the Almighty said: O son of Adam, so long as you call upon Me and ask of Me, I shall forgive you for what you have done, and I shall not mind. O son of Adam, were your sins to reach the clouds of the sky and were you then to ask forgiveness of Me, I would forgive you. O son of Adam, were you to come to Me with sins nearly as great as the earth and were you then to face Me, ascribing no partner to Me, I would bring you forgiveness nearly as great at it." Sheikh G.F. Haddad said:
"Allah Most High promised high levels to the repentant and He mentioned that the Throne-bearing angels make repentance for them also. And the Prophet, upon him peace, gave us glad tidings with regards to the believer's sins precisely because they lead to repentance. Therefore continue to repent!" Your finding it hard to repent is because you do not trust in yourself and perhaps even find it humiliating. This is what the ego hates and it is a good sign for redoubling repentance. A broken heart is better than a pleased one, so never stop repenting.

Sin or no sin we despair in ourselves: "The whole matter consists in seeing yourself as a disobedient servant without a single good deed" (Sheikh  Ibrahim al-Dusuqi). Our hope is all taken up in Allah:

{ Say: O my servants who have transgressed against their souls. Despair not of the Mercy of Allah: for Allah forgives all sins: He is Oft-Forgiving, Most Merciful }(Zumar 39:53)."

So you must put the word of Allah above your feelings of desperation. The doubt in your mind that prevents you from repenting is the whisperings of shaytan, because he knows that Allah is the most forgiving and loves sincere repentance. The worst thing you can possibly do is to stop repenting.
"We should not divinize our sins. They have no power over us and millions of them can be erased in one instant of sincerity accepted by Allah. We should look for that instant. Where else than in repentance? It is our stairwell, if the angels were to envy us it would be for that."

"Will power is built up by habit over time. Change your routine for a few weeks. Do something new and leave something out. One of the Sheikhs  said, if it is too hard to clear the garbage, build a bridge over it and move on. This is good advice." Similarly, salah over time bears the fruit described in the blessed verse:

{"Prayer restrains from shameful and unjust deeds"} (Ankabut 29:45).

In time, we should not get stuck forever at the station of weakness. Invoke blessings on the Prophet together with saying a staghfirullah x100 daily. Make it incumbent upon yourself to do "something special" for Allah Most High."

This wise counsel by Sheikh Gibril should help you understand that no matter how severe our sins, the very worst thing we can do is despair of Allah's mercy and forgiveness. You have simply allowed - through erroneous belief - your sins to take control over you. In effect, they have become your controller and your god. Yet, the word of Allah is crystal clear - do not despair of my mercy! Brother, you obviously are sincere in your repentance and regret for your sins, so put your trust in Allah's promise and get back to the life of repentance and forgiveness, and trust that Allah will forgive you, in sha' Allah ,Your limiting self is destroying you right now because you have allowed something other than Allah to dictate your thoughts, feelings and affairs. You are your own worst enemy, and you have to accept the fact that you sinned, surrender to it and move on by asking for Allah's forgiveness and trying your best to never do it again. Use this as a source of renewing your iman (faith) and your desire to be close to Allah. Transform this dark spot in your life to strength and a source of renewal. Use it to enter a new realm of intimacy with Allah by spilling your heart out to Him - all your fears, your doubts, your pain, whatever - let Him hear it and confide in Him. This is what He wants and what He loves. Then you will - ` in sha' Allah  - begin to see the purpose in everything that Allah wills, even that which we deem to be 'bad'. From the bad, Allah brings out the good, which is what He wants - for us to know Him as limitless Goodness!

"Peace with God implies accepting all things as from Him, and a fearless willingness to investigate all things as from Him. Then there is no fear that there is something "not" from Him, somewhere that we should "not" go, a dark closet in which something fearful may lurk" (Ali Ansari).

Allah says in a Hadith Qudsi that He is as His servants think He is. Right now, you choose to see Allah only as a punisher, but that is by your choosing. You have the ability inside you to see Allah how He wishes us to see Him, which I have illustrated above through various Qur'anic  ayah and Hadith . We don't begin everything we do in Islam with "In the Name of Allah, the Punisher, the Avenger", do we? We begin with Allah, the most Gracious, the most Merciful. Allah's punishment right now is your own self-loathing, which is destroying your spirit and will. But you always have the opportunity and ability to get beyond it through the gift of repentance and forgiveness. We must learn to forgive ourselves in order for Allah to forgive us. If we cannot, we will go on living our lives in denial of Allah's mercy and forgiveness, which in and of itself is a horrendous sin perhaps even worse than the actual sin committed at the outset! Don't make that mistake by denying Allah's overwhelming mercy and goodness.

In regard to your parents, the best thing you can do for them is to understand them and in the most gentle and respectful of ways, try to show them a better way. The gift of Islam is the gift of knowledge of Truth, which can be granted to anyone, young or old. However, the one that receives this gift has an amanah, or a responsibility to use it for the benefit of others, for Allah's sake. As such, you have insight into some of your parent's ways that are perhaps not healthy for the family and you find it difficult. Since you have been blessed with this insight, try to help them to see things in a different light. Again, however, do it with the utmost respect and love. Be patient and look for the right opportunities and times that you think will optimize the possibility of them being receptive to the knowledge. `in sha' Allah, you can help your parents to do things in a better way thereby helping your entire family.
 

All the best to you….