Is it permissible to marry someone who touched me after I swore an oath that he would not touch me, and what is the expiation for this oath?

You committed a sin by engaging in an illicit relationship with a foreign man. You must repent to Allah and immediately sever the relationship. Regarding your oath: if your intention was only to prevent him from illicit touching, then you have not broken your oath if he did not touch you before the marriage contract, and it is permissible for you to marry him, because an oath is based on the intention of the one who swears it. However, if you intended not to marry him in the future, then you must offer expiation for your oath (kaffarat yamin (definition)) if you marry him. This is preferable if he is a man of good character and religious commitment, for the Prophet, peace and blessings be upon him, said: "Whoever swears an oath, then sees something else as better than it, let him offer expiation for his oath and do that which is better."