Salaam,
I am a woman married since 3 years.due to my ignorance I had an haraam relationship with a guy and my husband caught it.but I asked his forgiveness and never repeated it again.after 1 year he says he can't forgive me ands ent me to my home.. I always seek repentance from allah.I love my husband back.I don't know what should I do.is there any dua to get him back

Just like some women can never forgive their husband for infidelity... some men can never forgive their wives for it either.

You can... and should try first... but you have to accept if he can't forgive you.

Hello Lonelyme,

Pray Astaghfar

Dua Astaghfar (Forgiveness) | Hadith of the Day

Guess he still not gave you talaq from your description. He might still loves you but it must be difficult for him to forget the past. I will suggest to be sincere and honest about your emotions with him and give him some time.