This was well and thoughtfully written. I don't usually care for infidelity fics, and I won't say I loved this, but I thought it was masterfully done. I love subtle writing, and little details that let you know what's going on, and you did that so incredibly well.
Your Severus was completely in character. I think someone else said note perfect, and I want to agree with that. I could tell just how much he cared for Harry with almost every gesture. And it rather made sense to me that this other lover meant little or nothing to him.
I sincerely appreciated how well this story was handled. I doubt a lesser writer could have pulled this off.