If Sullivan was gonna enact revenge on Benoit for 'stealing' his woman, why would he wait ten years to do it? I can only imagine how angry one must get when their wife/girlfriend leaves them for another man (especially for Sullivan to make even a passing remark about how he wanted to kill Benoit over it) but as with all people who have had wives/girlfriends leave them for another man, he would have calmed down overtime.
Also, to my knowledge he was never confirmed to be a Satanist. It's all gossip and rumors (in a business that is full of them) based off the fact that he once had a devil-worshiping gimmick that he supposedly got too invested in. Even if he were a card carrying member of Satanism, that doesn't automatically indicate that he is anymore capable or prone to committing violent acts than anyone else is.