I actually used to think about them together and literally made myself vomit

Yeah been there. All ya can do is what your doen just stop those thoughts when they happen. I drove by where the OM lives the other day for the first time(I had to for work not snooping). I spent the rest of the day not feeling well and picturing them there together. In a way I think its ok to let these thoughts happen but ONLY for a short time,, say give yourself 20 min to think them through then STOP. Ussually after the given time I dont feel any better and can soon realize that thinking those thoughts at all is pointless,, just causes grief or anger. Which brings me back to the just STOP thinking those thoughts. Easy to say but it can be done with practice. It sounds like you have allreaddy figured this out as well but hopefully it helps to know others go through the same stuff.
keep trying.