He doesn't .l. anymore?

So basically, my boyfriend doesn't get hard around me anymore for some reason. Normally, we just kissed and he was rockhard, but for the past weeks things have been weird. He is more of a top guy and when we tried doing stuff, he couldn't keep it up for the whole time and eventually didn't even come. Anyone has an explanation or some advice? I am getting a little desperate here.. -.- Thanks!