It's difficult for me to rate, as in the first half of the story I couldn't relate to the MCs, that got better in the second half. Additionally the whole story centered around the BDSM stuff - who did what to whom and with what, all the mechanics. I missed learning more of Justin and Tobias - was it mentioned what profession they have? Don't remember. And why the constant need of other people in their relationship? No clue. For me even the end wasn't surprising.
So overall it's 2 stars for me.