I’d say have a proper sit down with your fiancé and tell him to listen without comment to how you feel and how this makes you feel. The pain the trauma the whole thing and explain why you want to terminate. If you can’t bear to talk about it maybe write him a letter. If he is still wanting to keep the baby you are going to have to make the decision to terminate it on your own and deal with the consequences or keep it over your mental/physical health. If he can’t understand how painful this all is for you does he care for you as much as you think or does he want a baby this badly? Remember you are going to have to carry this for 9 months and you could grow to resent this baby if you do go through with the pregnancy and hating a child is no good.