Susan,

When you say by a Christian, I assume your second union was outside the Catholic Church.

Since marriage is indissoluble, that second union is presumed to have been invalid because the original marriage was never declared null and void. Hence, you would have to recognize the second union objectively as adulterous.

Since this man has passed away, you are not presently living objectively in sin so that impediment to receiving Holy Communion is no longer present, however, if you understood the severity of the sin and freely went though with it anyway, that is the recipe for mortal sin. This, too, is an impediment to receiving Communion, until or unless there is a sincere Sacramental Confession.

If you are serious about being reconciled to God and His Church and receiving Jesus in the Eucharist, my suggestion would be to encounter Jesus in the Sacrament of Confession about this whole saga.

If you are not so inclined, then make an appointment to see the pastor to explain the whole situation or perhaps doing both would be a good idea.

Peace,

Paul