Rules Regarding Oath (Qasam)
2679. If a person takes an oath that he will perform an act (e.g. that he will fast) or will refrain from doing an act (e.g. that he will not smoke), but does not intentionally act according to his oath, he should give Kaffarah for it, which means he should set a slave free, or should fully feed ten indigent persons, or should provide them with clothes. And if he is not able to perform these acts, he should fast for three consecutive days.
The oath must be sworn by one of those names of the Almighty Allah which are exclusively used for Him, (e.g. 'Allah'). And even if he swears by a name which is used for other beings also, but is used so extensively for Him, that when any person utters that name one is reminded of Him Alone, for example, if he swears by the name Khaliq (the Creator) and Raziq (the Bestower), the oath will be in order. In fact, if he uses other names or attributes of Allah, which do not remind of Him, but give that connotation when used during an oath, like Samee' (All Hearing) or Baseer (All Seeing), even then the oath will be valid
As for as Forgiveness concern yes it true that Almighty Allah is Most Merciful and we should have hope in His Mercy but same time we should realise our faults and be ashamed that you are already said and it’s best thing if a person feels guilty after committing any Sin it means his Instinct alive and this is one of the blessings of Allah otherwise if nauzobillah a day comes in once life that he/she after commuting gunah doesn’t feel bad it means he/she has Wrath of Allah and his/her Zameer (instinct) had died.
So just do Isteghfar and leave it on Allah don’t get stress otherwise it will destroy your life. Just ask for forgiveness and cry then leave it upon Allah.