Why am i finding it difficult to let go? :(
You have invested time, energy and emotions in this. That's why. Perhaps it is not in your nature to treat people so badly and so you find it hard to believe that he will continue this behaviour afterwards.
You need to follow your gut instincts. If you feel something is not right, you are mostlikely right. Like someone else said, this is your chance.
I would like to know what you are thinking. Do you think he will treat you better when you are married? Will you be moving to another country to live with him? Do you think things will be completely different when you are married and living together under the same roof? I would like to know, so please tell me.