Was it something I did?

Alright. So my boyfriend and I have only been together a few months now, and we finally had sex a couple weeks ago. In the heat of the moment, (after a few attempts at giving him head) for whatever reason, he couldn't maintain a hard on.. Since then, we have not tried to have sex again/do anything else sexual... In the past I have always gotten him off with just blow jobs, so I know that wasn't a factor in this.. We act normal, still make out and all that, calls me all the time, tease each other occasionally, we go on dates still so it's like nothing has changed between us..