Yes, I think you definitely have to sit down and be as candid with him as he is with you but I do know you have to look at him, not his father. We are not 100% (or even 50/50) our parents. You can't know what he will be like in the future or what children will be like or any of that with anyone!

Yes it will/should take you awhile to get use to this big news but it doesn't have to change how you feel about him. If he wants a romantic relationship with you and you do not, I think you have to break it off completely. You are not responsible for how he feels or is, you can only be responsible for yourself and if you don't want to marry him and that's what he wants, there is no "middle" ground there and hanging on looks to only make yourself feel better, impedes his growth, as he would probably be thinking eventually you would come around to his way of thinking.