What is the ruling of the Sharia upon me in this situation, and will I be sinful if I file a lawsuit?

You erred by leaving your husband's house without his permission, merely because of an agreement to divorce, and this makes you disobedient (nashiz). Your husband is not permitted to leave you in limbo; he must either retain you with kindness or release you with grace. You have the right to file a lawsuit, but it is better for the wise individuals from both families to sit together for reconciliation, because reconciliation is best and "divorce often has negative consequences, especially if the couple has children." If reconciliation is impossible, then there is no harm in divorce, for Allah "will enrich each from His abundance," and "He may destine for the man a woman who will be a comfort to his eyes, and for the woman one who will provide generously for her."