I think the sex happened on the same day and moment that he confessed.. so after that the emotions risen then that happened.. then afterward, she regretted it..
Now that you had lost your feelings for him.. There are times that you might feel awkward when you're together.. cause it happened to me before (I will not say the details but a little same with your experience) and after that, I kind of avoided him and when I talked to him there's the distance and he noticed that.. but we did managed to fix that before our graduation (college). And now, we're ok and just laughing on that whenever we talk about it.