I had been separated from my husband for over a year, when I slept with someone, it happened 4 times and each time I regretted it straight away but went back for more... He finally stopped it and I went running back to my husband, I stayed with my husband for 3 months and then we separated again, in this time I had 2 miscarriages (my husbands) I felt almost like the miscarriages were my punishment for sleeping with someone else, even though I didn't want to be pregnant, it hurt when I miscarried. I still feel that I have not been forgiven and that maybe I never will!
I know it is the worst sin to be committed and I am disgusted with myself even now 2 years later! It almost feels like it never happened but each time I remember I am filled with regret and repent by asking for forgiveness from Allah.
I only wished I had thought about the punishment in the grave and in the hereafter before I committed the sin. But I couldn't think about anything but him at the time.
My husband does not know and we are still separated.
I do not see or talk to the man and I try to do good deeds so that they will out way the bad but adultery is a very big deed to out-weigh by many good ones.
What should I do? What else can I do?

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.

Adultery is a major sin and it is an abominable one. Allah warned us against committing Zina/adultery or fornication saying (interpretation of meaning): "And come not near to the unlawful sexual intercourse. Verily, it is a Fâhishah [i.e. anything that transgresses its limits (a great sin)], and an evil way (that leads one to Hell unless Allah forgives him). (Al-Isra 17:32)

It (Zina) is a pleasure of an instant, and regret for a lifetime.

You did well by repenting. So do good deeds in the future and perform them as much as you can, avoid any means that could lead you to commit Zina again, like not being dressed in Hijab, looking at what is forbidden, or being in seclusion with a man and the like.

You have to know that the Mercy of Allah is boundless; He likes His servant to repent, and He is the One Who enables people to repent and it is He Who accepts repentance. Allah says (interpretation of meaning): "Say: "O 'Ibâdî (My slaves) who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allâh, verily Allâh forgives all sins. Truly, He is Oft-Forgiving, Most Merciful. (Az-Zumar 39:53)

So, do not despair of the Mercy of Allah, and think good of Him, as Allah helps those who think good of Him.

We advise you to reconcile with your husband and supplicate as much as possible so that Allah may re-unite you.

Allah knows best.