Alex has never not known where Billie was, even when they weren't talking he knew she was in hell with Lucifer so he will be losing his fucking mind. And Clary won't really notice I'm sure, she'll be too tired. And she'll know it's just all around a stressful time. And Billie will look at him like, "I would have been back sooner, but Lucifer wanted to make sure this vessel could withstand me." And she will look at everyone in the room. "What exactly has happened? Nothing even feels right."

Oh yes, and Darren being thr slippery skeezeball he is will use it to his advantage. I could even seeing him walking up to Billie in front of everyone and the other demons making sure that their conversation is kept between just them. And when he offers her a place oh... it will be bad.