Thank you! I think the longer he senses his mate is within reach, the more the Incubus controls Snape, master Occlumens or no. So his possessiveness just grows irrationally.
I like to imagine that although the attractive Snape affected Harry that way, it was just the way the Incubus caught his attention and he will grow to love both looks of Snape or better yet, grow to love the man no matter the face :) (But the sexy face will help while he grows thicker skin to deal with that sharp humour...)