Is three days of fasting sufficient as expiation for an oath, after breaking it, knowing that had the one who swore the oath known of the circumstances in which I broke it, he would have excused me?

If a person takes an oath to another, the intention behind this oath refers back to the one who requested the oath (the mustahlif). So, if his intention was to restrict the oath to a specific time, person, or place, then the one who took the oath (the halif) does not break it unless he violates the intention of the mustahlif. If there was no intention on the part of the mustahlif, but there were circumstantial indicators (qara'in) suggesting a restriction of the oath, then the oath is restricted by that indicator.

Therefore, if there is an indicator suggesting that the mustahlif intended the abstinence from updating for a specific period, you do not break the oath if you do not do the sworn-upon act during that period. However, if there is no indicator and no intention on the part of the mustahlif, then you break the oath according to its apparent meaning, and whoever breaks an oath must offer an expiation for an oath (kaffarat yamin).