Severus Snape has a secret. Even though he was friends with Lily, and he cared for her, he could never love her because he was into men. More specifically, he was into James Potter. As little sense as it made, he'd always found the Gryffindor boy very attractive. The two grew up, and a lot happened between them. When Severus turned spy, he was actually quite surprised at how much James had changed. He was pleased to find out James liked men too, but he could never bring himself to make a move. And then, the Potters are killed (or so he thinks)
James returns after being hidden away by Dumbledore. Seeing him again brings all the old feelings back, but Severus' relationship with Harry complicates things. Dare he make a move this time, and get what he's always wanted?
I would play James and Harry. PM me if interested in hashing out the details.