And you know, sometimes orgasms are like little blips on the radar screen, and afterwards you're like, "That was it?" And other times you cum and cum and cum and it's cataclysmic. But it's just natural that the earth doesn't move every time we have sex. I would guess that that usually happens when our minds are a little bit elsewhere or we're too focused on the outcome and wanting a certain result, instead of connecting on a heart level, beyond the physical.
And if the intensity of your feelings for him scared you, it makes sense that something was off. It could just have been a way for you to subconsciously tell yourself to slow down a bit because it was overwhelming you. Next time you're together, try something new or pace yourself. Sometimes I find that slowing everything down helps me really get into the sensations, enjoying every delicious moment, and enables me to observe my emotions and not get bowled over by them.