Are you at a point in your life that you feel like you need to settle for someone like him? This is a MAJOR red flag. He's obviously not mature enough emotionally to be getting married. Don't throw your life away.

How much have you invested in this relationship? Was there some sort of arrangement through the families and he just ended up growing on you to the point you'd want to marry him?

Watching pornography is certainly considered a vice, but he's done something beyond that. He's sought out a connection, whether emotional or physical, with someone other than yourself.

If you're so desperate to forgive such a grievous offense, then so be it, otherwise, RUN!