All sins can be forgiven by sincere repentance. Almighty Allah said: “Despair not of the mercy of Allah, Who forgives all sins. Lo! He is the Forgiving, the Merciful”. Yes, it is recommended to seek forgiveness whenever the committed sins are remembered but should not turn into psychological complication.
Yes, it is permissible to live like that as marriage is highly recommended and not compulsory, although Islam strongly recommends it in many narrations, like when the Messenger of Allah (peace be upon him) said: "There is no deed in Islam that Almighty Allah loves more than marriage."