Regrettably, many marriages having difficulty are dissolved in civil tribunals. Civil divorce in and of itself does not automatically bar Catholics from receiving the sacraments. But because the Church holds the bond of marriage as an indissoluble bond, sacramentally witnessing to the undissoluable covenant of fidelity between God and His Church, remarriage is not possible within the Church unless it can be proven that some fundamental element of marriage was lacking on part an earlier attempt at marriage.
Additional information about resources available in the diocese for divorced persons can be found here.
-- Diocesan Links --
FAQ on Marriage Processes: Dissolution and Nullity (via the Diocesan Tribunal) Catholic Times Article on Marriage Annulments
FAQ About Tribunal Processes (via the Diocesan Tribunal)
-- External links --
Answering Common Questions about Annulments — Edward Peters via Catholic Answers