① "我甚至根本不知道做他的朋友是什么样子," This sentence is good though it seems not quite natural to native speaker.
② “我们从来没做过朋友而已” is a bit confusing to me. Because you used the word 'just' adds a feeling that implies this person has always been more than just a friend. But, I didn't find it on the sentence. So, recommend to say: 我们从来都不仅是朋友。