I suggest you are new here?
You will find out with time that people will answer your question, and also debate around it, and expland some of the points made - as has happened on this thread.
You began by asking why your boyfriend was so freaked out at the thought that you were pregnant.
This is a man who declined to protect you from pregnancy even after you asked him so to do - and you then permitted intercourse whuch could very probably have led to pregnancy.
You then wondered why this man was so upset at the thought of fatherhood.
You are both old enough (I assume he is of a similar age) to be able to approach sex and its consequences in an adult manner instead of pretending that the concept of unproteced sex resulting in pregnancy is something that only happens on TV.
After the thread commenced, you referred to him knowing you were not prtected, but 'he' - it was actually both of you - continued to have sex, and you say 'what can you do??'
You could try saying No, I don;t want to risk getting pregnant, so no condom, no sex - and since you are the person in this relationship who will conceive and birth the baby, that is yoiur absolute right - which you chose not to exercise.
I repeat, you took a dangerous risk, and got away with it, but your apparent lack of understanding of your partner's reactions suggests that he is certainly not ready for children - or indeed marriage, and you should think again before embarking on either course with him.
You both need to understand the concepts of adult behaviour before you embark on taking this relationship any further, and in case you have not learned the message - unrprotected sex is designed to lead to pregnancy - get your boyfriend a biology book, and tell him to grow up as well.