Why does "it" suddenly turn off.?

Okay so, I was TRYING to have sex with my new boyfriend now.. & well okay I sucked his dick & he ate me up... but when he was tryna put his dick inside me.. it just turned off.. am I doing something wrong.? It was hard when I sucked it but all of a sudden in a snap it wasn't hard anymore. He even apologized a lot & said "I was into it but my body wasn't.?" What do I do now, it was kinda awkward. This is the second time & second guy it happened with... the last time I had sex was probably a good 2-3 years ago. Have I lost my touch.? Lol