I am searching for more information on how & when is it admissible for a man to remarry while his first wife is still alive.

According to Shari'a, a Muslim male may have four wives simultaneously with the condition of maintaining equality among all his wives. Therefore, in principle, you can remarry without divorcing your wife.

However, in order to avoid bitter feelings to your present wife, you should first discuss your intentions of remarrying with wisdom. That will save you from the negative consequences fo betrayal, etc. being possibly expressed by her upon her discovering your secret remarriage.

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai
FATWA DEPT.