cum...

soy boyfriend and I were having sex this.one time and he wisperd in my ear and said "cum for me baby" and I don't understand like yes...I know what cum is and I know what it feels like but how would he know if I even cumed or not?like do guys just know because we were having intercorse when he said that and I was just thinking maybe he will know if I came when I'm wetter and moaning but...what does that do for him? how does that pleasure him I'm sorry I just don't understand.