Is it permissible to break off an engagement because your fiancée rode in a car with a male colleague, along with other women, after work due to unavailability of transportation?

The Muslim woman is commanded to remain in her home, raise her children, and care for her husband and family. If she is compelled to work outside the home, she must not mix with men. If she cannot find any other option, and she adheres to the Shari'ah guidelines, such as wearing the hijab and speaking only when necessary, then there is no harm. Your fiancée riding in a car with two men while another woman is present does not constitute an unlawful khalwa (private seclusion) and does not necessitate breaking off the engagement. However, she should avoid it if she does not need to, and abandon it after marriage.