and that you already listed out the things that you want to say. tell him/her to not panic about what you are going to say. tell him/her to listen carefully and be open-minded about it. but if he/she is really your true friend, he/she will understand you and the two of you will get through it. the result of your emotional sharing will make you feel better, whether taking up your relationship to the next level is the right choice or not.
however, when he/she says no, do not feel bad about it. maybe he/she really loves you and cares for you a lot but only as a friend. understand him/her 