I have ruined my engagement.
How have you ruined it?
I had sex with other men.
It is wrong to cheat on your partner when you are engaged. If you can't honor the commitment, you should break up with your partner.
It is too late to break up now.
It is not too late to break up. You should have not cheated on your partner like that once you were engaged. You need to tell him what happened and see where it goes from there.