Is it obligatory for the questioner to move to a non-mixed university in Saudi Arabia, or to continue studying and engaging in da‘wah (proselytizing) efforts in his current country, especially since the environment of his university is not bad and there are many religious people there?

All praise is due to Allah, who has blessed you with repentance. We believe you should leave your studies at this mixed university and transfer to study in Saudi Arabia. If you move there, Allah will compensate you for the righteous company you associated with in your country, for devout young people are numerous in that land. Benefit from your time there by acquiring beneficial knowledge, for it is one of the best means of drawing near to Allah and a cause of steadfastness and guidance. If you return to your country bearing knowledge, your brothers will greatly benefit from you in calling to Allah. And Allah knows best.