If I am facing abuse from my husband, can the Church allow me to divorce him or would that be sinful?
It can never be sinful to use reasonable means to try and save one’s life. So no, it is not sinful to leave a spouse if he poses physical danger to his wife and maybe the children. When one has exhausted means of fixing this situation, the woman may leave. The Code of Canon Law says:
A spouse who occasions grave danger of soul or body to the other or to the children, or otherwise makes the common life unduly difficult, provides the other spouse with a reason to leave, either by a decree of the local ordinary [e.g., bishop] or, if there is danger in delay, even on his or her own authority. (CIC 1153)
However it is to be noted that once such danger has been averted (which rarely happens in such abuse cases), the family common life has to be restored. One should use every means at their disposal to work on the marriage, but first has to consider safety.
Marriage by it’s nature cannot be dissolved, so getting a divorce is only equivalent to a legal separation and the Church tolerates this for the safety of lives. So, the people who are divorced are still considered validly married by the Church and cannot validly contract another marriage unless an annulment is granted.
Please if you are facing abuse in your home, do not be silent as you could be in real danger. You have to seek help quickly. You could contact your priest or a trusted professional for advise on how to deal with it.