Very enjoyable and touching. The gradually unravelling mystery and the alternating timelines were cleverly done. I agree with Minerva: the forced politeness was most entertaining, as was the rest of the dialogue.
I loved the energetic foreplay bickering at the beginning, Severus’ panic and Harry’s rash decision after their night together, the revealing trip to the Infirmary (so cute and hilarious), Harry’s calm behaviour when he confronted Severus.
The last line rounded off the issue of trust beautifully. So many other wonderful lines, too. I'm particularly fond of this one:
Another fat tear falls artistically from Potter’s lashes as he nods.