Jebus, people. Should he start wearing a scarlet "A" or something? Is he not "pure" anymore??
It does suck, but it's just sex. Maybe not even the first time, if the .5 is to be believed (spoilers, maybe? It's the next chapter)
EDIT: Just realized I explained my point pretty horribly. I meant it more that it was a violation he couldn't do anything about, and he's not lesser for it. I also hope the succubus burns slow for it.
Additional EDIT: I really, really hope this wasn't just some way the author could 'pop' MC's cherry, so he can go full throttle with sex with the other girls without worrying about choosing (which he kind of already did)...